diff --git a/lib/kolab_sync_backend_common.php b/lib/kolab_sync_backend_common.php
index 018ee15..06e0fbb 100644
--- a/lib/kolab_sync_backend_common.php
+++ b/lib/kolab_sync_backend_common.php
@@ -1,277 +1,279 @@
 <?php
 
 /**
  +--------------------------------------------------------------------------+
  | Kolab Sync (ActiveSync for Kolab)                                        |
  |                                                                          |
  | Copyright (C) 2011-2012, Kolab Systems AG <contact@kolabsys.com>         |
  |                                                                          |
  | This program is free software: you can redistribute it and/or modify     |
  | it under the terms of the GNU Affero General Public License as published |
  | by the Free Software Foundation, either version 3 of the License, or     |
  | (at your option) any later version.                                      |
  |                                                                          |
  | This program is distributed in the hope that it will be useful,          |
  | but WITHOUT ANY WARRANTY; without even the implied warranty of           |
  | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the             |
  | GNU Affero General Public License for more details.                      |
  |                                                                          |
  | You should have received a copy of the GNU Affero General Public License |
  | along with this program. If not, see <http://www.gnu.org/licenses/>      |
  +--------------------------------------------------------------------------+
  | Author: Aleksander Machniak <machniak@kolabsys.com>                      |
  +--------------------------------------------------------------------------+
 */
 
 /**
  * Parent backend class for kolab backends
  */
 class kolab_sync_backend_common implements Syncroton_Backend_IBackend
 {
     /**
      * Table name
      *
      * @var string
      */
     protected $table_name;
 
     /**
      * Model interface name
      *
      * @var string
      */
     protected $interface_name;
 
     /**
      * Backend interface name
      *
      * @var string
      */
     protected $class_name;
 
     /**
      * SQL Database engine
      *
      * @var rcube_db
      */
     protected $db;
 
     /**
      * Internal cache (in-memory)
      *
      * @var array
      */
     protected $cache = array();
 
 
     /**
      * Constructor
      */
     function __construct()
     {
         $this->db = rcube::get_instance()->get_dbh();
 
         if (empty($this->class_name)) {
             $this->class_name = str_replace('Model_I', 'Model_', $this->interface_name);
         }
     }
 
     /**
      * Creates new Syncroton object in database
      *
      * @param Syncroton_Model_* $object Object
      *
-     * @throws InvalidArgumentException
      * @return Syncroton_Model_* Object
+     * @throws InvalidArgumentException|Syncroton_Exception_DeadlockDetected|Exception
      */
     public function create($object)
     {
         if (! $object instanceof $this->interface_name) {
             throw new InvalidArgumentException('$object must be instance of ' . $this->interface_name);
         }
 
         $data = $this->object_to_array($object);
         $cols = array();
 
         $data['id'] = $object->id = sha1(mt_rand(). microtime());
 
         foreach (array_keys($data) as $key) {
             $cols[] = $this->db->quote_identifier($key);
         }
 
         $result = $this->db->query('INSERT INTO `' . $this->table_name . '`' . ' (' . implode(', ', $cols) . ')'
             . ' VALUES(' . implode(', ', array_fill(0, count($cols), '?')) . ')',
             array_values($data)
         );
 
         if ($err = $this->db->is_error($result)) {
-            //Deadlock detected
+            $err = "Failed to save instance of {$this->interface_name}: {$err}";
             if ($this->db->error_info()[0] == '40001') {
-                throw new Syncroton_Exception_DeadlockDetected('Failed to save instance of ' . $this->interface_name . ": " . $err);
+                throw new Syncroton_Exception_DeadlockDetected($err);
             } else {
-                throw new Exception('Failed to save instance of ' . $this->interface_name . ": " . $err);
+                throw new Exception($err);
             }
         }
 
         return $object;
     }
 
     /**
      * Returns Syncroton data object
      *
      * @param string  $id
      * @throws Syncroton_Exception_NotFound
      * @return Syncroton_Model_*
      */
     public function get($id)
     {
         $id = $id instanceof $this->interface_name ? $id->id : $id;
 
         if ($id) {
             $select = $this->db->query('SELECT * FROM `' . $this->table_name . '` WHERE `id` = ?', array($id));
             $data   = $this->db->fetch_assoc($select);
         }
 
         if (empty($data)) {
             throw new Syncroton_Exception_NotFound('Object not found');
         }
 
         return $this->get_object($data);
     }
 
     /**
      * Deletes Syncroton data object
      *
      * @param string|Syncroton_Model_* $id Object or identifier
      *
      * @return bool True on success, False on failure
+     * @throws Syncroton_Exception_DeadlockDetected|Exception
      */
     public function delete($id)
     {
         $id = $id instanceof $this->interface_name ? $id->id : $id;
 
         if (!$id) {
             return false;
         }
 
         $result = $this->db->query('DELETE FROM `' . $this->table_name .'` WHERE `id` = ?', array($id));
 
         if ($err = $this->db->is_error($result)) {
-            //Deadlock detected
+            $err = "Failed to delete instance of {$this->interface_name}: {$err}";
             if ($this->db->error_info()[0] == '40001') {
-                throw new Syncroton_Exception_DeadlockDetected('Failed to delete instance of ' . $this->interface_name . ": " . $err);
+                throw new Syncroton_Exception_DeadlockDetected($err);
             } else {
-                throw new Exception('Failed to delete instance of ' . $this->interface_name . ": " . $err);
+                throw new Exception($rr);
             }
         }
 
         return (bool) $this->db->affected_rows($result);
     }
 
     /**
      * Updates Syncroton data object
      *
      * @param Syncroton_Model_* $object
      *
-     * @throws InvalidArgumentException
      * @return Syncroton_Model_* Object
+     * @throws InvalidArgumentException|Syncroton_Exception_DeadlockDetected|Exception
      */
     public function update($object)
     {
         if (! $object instanceof $this->interface_name) {
             throw new InvalidArgumentException('$object must be instanace of ' . $this->interface_name);
         }
 
         $data = $this->object_to_array($object);
         $set  = array();
 
         foreach (array_keys($data) as $key) {
             $set[] = $this->db->quote_identifier($key) . ' = ?';
         }
 
         $result = $this->db->query('UPDATE `' . $this->table_name . '` SET ' . implode(', ', $set)
             . ' WHERE `id` = ' . $this->db->quote($object->id), array_values($data));
+
         if ($err = $this->db->is_error($result)) {
-            //Deadlock detected
+            $err = "Failed to update instance of {$this->interface_name}: {$err}";
             if ($this->db->error_info()[0] == '40001') {
-                throw new Syncroton_Exception_DeadlockDetected('Failed to update instance of ' . $this->interface_name . ": " . $err);
+                throw new Syncroton_Exception_DeadlockDetected($err);
             } else {
-                throw new Exception('Failed to update instance of ' . $this->interface_name . ": " . $err);
+                throw new Exception($err);
             }
         }
 
         return $object;
     }
 
     /**
      * Returns list of user accounts
      *
      * @param Syncroton_Model_Device $device The current device
      *
      * @return array List of Syncroton_Model_Account objects
      */
     public function userAccounts($device)
     {
         // this method is overwritten by kolab_sync_backend class
     }
 
     /**
      * Convert array into model object
      */
     protected function get_object($data)
     {
         foreach ($data as $key => $value) {
             unset($data[$key]);
 
             if (!empty($value) && preg_match('/^\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}/', $value)) { // 2012-08-12 07:43:26
                 $value = new DateTime($value, new DateTimeZone('utc'));
             }
 
             $data[$this->to_camelcase($key, false)] = $value;
         }
 
         return new $this->class_name($data);
     }
 
     /**
      * Converts model object into array
      */
     protected function object_to_array($object)
     {
         $data = array();
 
         foreach ($object as $key => $value) {
             if ($value instanceof DateTime) {
                 $value = $value->format('Y-m-d H:i:s');
             } elseif (is_object($value) && isset($value->id)) {
                 $value = $value->id;
             }
 
             $data[$this->from_camelcase($key)] = $value;
         }
 
         return $data;
     }
 
     /**
      * Convert property name from camel-case to lower-case-with-underscore
      */
     protected function from_camelcase($string)
     {
         $string = lcfirst($string);
 
         return preg_replace_callback('/([A-Z])/', function ($string) { return '_' . strtolower($string[0]); }, $string);
     }
 
     /**
      * Convert property name from lower-case-with-underscore to camel-case
      */
     protected function to_camelcase($string, $ucFirst = true)
     {
         if ($ucFirst) {
             $string = ucfirst($string);
         }
 
         return preg_replace_callback('/_([a-z])/', function ($string) { return strtoupper($string[1]); }, $string);
     }
 }
diff --git a/lib/kolab_sync_backend_content.php b/lib/kolab_sync_backend_content.php
index 83298af..36432cb 100644
--- a/lib/kolab_sync_backend_content.php
+++ b/lib/kolab_sync_backend_content.php
@@ -1,135 +1,138 @@
 <?php
 
 /**
  +--------------------------------------------------------------------------+
  | Kolab Sync (ActiveSync for Kolab)                                        |
  |                                                                          |
  | Copyright (C) 2011-2012, Kolab Systems AG <contact@kolabsys.com>         |
  |                                                                          |
  | This program is free software: you can redistribute it and/or modify     |
  | it under the terms of the GNU Affero General Public License as published |
  | by the Free Software Foundation, either version 3 of the License, or     |
  | (at your option) any later version.                                      |
  |                                                                          |
  | This program is distributed in the hope that it will be useful,          |
  | but WITHOUT ANY WARRANTY; without even the implied warranty of           |
  | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the             |
  | GNU Affero General Public License for more details.                      |
  |                                                                          |
  | You should have received a copy of the GNU Affero General Public License |
  | along with this program. If not, see <http://www.gnu.org/licenses/>      |
  +--------------------------------------------------------------------------+
  | Author: Aleksander Machniak <machniak@kolabsys.com>                      |
  +--------------------------------------------------------------------------+
 */
 
 /**
  * Kolab backend class for content storage
  */
 class kolab_sync_backend_content extends kolab_sync_backend_common implements Syncroton_Backend_IContent
 {
     protected $table_name     = 'syncroton_content';
     protected $interface_name = 'Syncroton_Model_IContent';
 
 
     /**
      * mark state as deleted. The state gets removed finally,
      * when the synckey gets validated during next sync.
      *
      * @param Syncroton_Model_IContent|string $id
      */
     public function delete($id)
     {
         $id = $id instanceof Syncroton_Model_IContent ? $id->id : $id;
 
         $result = $this->db->query("UPDATE `{$this->table_name}` SET `is_deleted` = 1 WHERE `id` = ?", array($id));
 
         if ($result = (bool) $this->db->affected_rows($result)) {
             unset($this->cache['content_folderstate']);
         }
 
         return $result;
     }
 
     /**
      * @param Syncroton_Model_IDevice|string $_deviceId
      * @param Syncroton_Model_IFolder|string $_folderId
      * @param string $_contentId
+     *
      * @return Syncroton_Model_IContent
      */
     public function getContentState($_deviceId, $_folderId, $_contentId)
     {
         $deviceId = $_deviceId instanceof Syncroton_Model_IDevice ? $_deviceId->id : $_deviceId;
         $folderId = $_folderId instanceof Syncroton_Model_IFolder ? $_folderId->id : $_folderId;
 
         $where[] = $this->db->quote_identifier('device_id') . ' = ' . $this->db->quote($deviceId);
         $where[] = $this->db->quote_identifier('folder_id') . ' = ' . $this->db->quote($folderId);
         $where[] = $this->db->quote_identifier('contentid') . ' = ' . $this->db->quote($_contentId);
         $where[] = $this->db->quote_identifier('is_deleted') . ' = 0';
 
         $select = $this->db->query("SELECT * FROM `{$this->table_name}` WHERE " . implode(' AND ', $where));
         $state  = $this->db->fetch_assoc($select);
 
         if (empty($state)) {
             throw new Syncroton_Exception_NotFound('Content not found');
         }
 
         return $this->get_object($state);
     }
 
     /**
      * get array of ids which got send to the client for a given class
      *
      * @param Syncroton_Model_IDevice|string $_deviceId
      * @param Syncroton_Model_IFolder|string $_folderId
+     * @param int                            $syncKey
+     *
      * @return array
      */
     public function getFolderState($_deviceId, $_folderId, $syncKey = null)
     {
         $deviceId = $_deviceId instanceof Syncroton_Model_IDevice ? $_deviceId->id : $_deviceId;
         $folderId = $_folderId instanceof Syncroton_Model_IFolder ? $_folderId->id : $_folderId;
-        $cachekey = $deviceId . ':' . $folderId;
+        $cachekey = $deviceId . ':' . $folderId . ':' . ($syncKey ?: '*');
 
         // in Sync request we call this function twice in case when
         // folder state changed - use cache to skip at least one SELECT query
         if (isset($this->cache['content_folderstate'][$cachekey])) {
             return $this->cache['content_folderstate'][$cachekey];
         }
 
         $where[] = $this->db->quote_identifier('device_id') . ' = ' . $this->db->quote($deviceId);
         $where[] = $this->db->quote_identifier('folder_id') . ' = ' . $this->db->quote($folderId);
+        $where[] = $this->db->quote_identifier('is_deleted') . ' = 0';
         if ($syncKey) {
             $where[] = $this->db->quote_identifier('creation_synckey') . ' < ' . $this->db->quote($syncKey + 1);
         }
-        $where[] = $this->db->quote_identifier('is_deleted') . ' = 0';
 
         $select = $this->db->query("SELECT `contentid` FROM `{$this->table_name}` WHERE " . implode(' AND ', $where));
         $result = array();
 
         while ($state = $this->db->fetch_assoc($select)) {
             $result[] = $state['contentid'];
         }
 
         return $this->cache['content_folderstate'][$cachekey] = $result;
     }
 
     /**
      * reset list of stored id
      *
      * @param Syncroton_Model_IDevice|string $_deviceId
      * @param Syncroton_Model_IFolder|string $_folderId
      */
     public function resetState($_deviceId, $_folderId)
     {
         $deviceId = $_deviceId instanceof Syncroton_Model_IDevice ? $_deviceId->id : $_deviceId;
         $folderId = $_folderId instanceof Syncroton_Model_IFolder ? $_folderId->id : $_folderId;
         $cachekey = $deviceId . ':' . $folderId;
 
         unset($this->cache['content_folderstate'][$cachekey]);
 
         $where[] = $this->db->quote_identifier('device_id') . ' = ' . $this->db->quote($deviceId);
         $where[] = $this->db->quote_identifier('folder_id') . ' = ' . $this->db->quote($folderId);
 
         $this->db->query("DELETE FROM `{$this->table_name}` WHERE " . implode(' AND ', $where));
     }
 }