diff --git a/plugins/calendar/calendar.php b/plugins/calendar/calendar.php
--- a/plugins/calendar/calendar.php
+++ b/plugins/calendar/calendar.php
@@ -2821,17 +2821,17 @@
     $noreply = $noreply || $status == 'needs-action' || $itip_sending === 0;
     $instance = rcube_utils::get_input_value('_instance', rcube_utils::INPUT_POST);
     $savemode = rcube_utils::get_input_value('_savemode', rcube_utils::INPUT_POST);
+    $comment  = rcube_utils::get_input_value('_comment', rcube_utils::INPUT_POST);
 
     $error_msg = $this->gettext('errorimportingevent');
-    $success = false;
-    $delegate = null;
+    $success   = false;
 
     if ($status == 'delegated') {
       $delegates = rcube_mime::decode_address_list(rcube_utils::get_input_value('_to', rcube_utils::INPUT_POST, true), 1, false);
       $delegate  = reset($delegates);
 
       if (empty($delegate) || empty($delegate['mailto'])) {
-        $this->rc->output->command('display_message', $this->gettext('libcalendaring.delegateinvalidaddress'), 'error');
+        $this->rc->output->command('display_message', $this->rc->gettext('libcalendaring.delegateinvalidaddress'), 'error');
         return;
       }
     }
@@ -2840,19 +2840,20 @@
     if ($event = $this->lib->mail_get_itip_object($mbox, $uid, $mime_id, 'event')) {
       // forward iTip request to delegatee
       if ($delegate) {
-        $rsvpme  = (bool) intval(rcube_utils::get_input_value('_rsvp', rcube_utils::INPUT_POST));
-        $comment = rcube_utils::get_input_value('_comment', rcube_utils::INPUT_POST);
+        $rsvpme = rcube_utils::get_input_value('_rsvp', rcube_utils::INPUT_POST);
+        $itip   = $this->load_itip();
 
-        $d_event = $comment ? array_merge($event, array('comment' => $comment)) : $event;
-        $itip    = $this->load_itip();
+        $event['comment'] = $comment;
 
-        if ($itip->delegate_to($d_event, $delegate, $rsvpme)) {
+        if ($itip->delegate_to($event, $delegate, !empty($rsvpme))) {
           $this->rc->output->show_message('calendar.itipsendsuccess', 'confirmation');
         }
         else {
           $this->rc->output->command('display_message', $this->gettext('itipresponseerror'), 'error');
         }
 
+        unset($event['comment']);
+
         // the delegator is set to non-participant, thus save as non-blocking
         $event['free_busy'] = 'free';
       }
@@ -3088,7 +3089,7 @@
 
     // send iTip reply
     if ($event['_method'] == 'REQUEST' && $organizer && !$noreply && !in_array(strtolower($organizer['email']), $emails) && !$error_msg) {
-      $event['comment'] = rcube_utils::get_input_value('_comment', rcube_utils::INPUT_POST);
+      $event['comment'] = $comment;
       $itip = $this->load_itip();
       $itip->set_sender_email($reply_sender);
       if ($itip->send_itip_message($event, 'REPLY', $organizer, 'itipsubject' . $status, 'itipmailbody' . $status))
@@ -3100,7 +3101,6 @@
     $this->rc->output->send();
   }
 
-
   /**
    * Handler for calendar/itip-remove requests
    */
diff --git a/plugins/tasklist/tasklist.php b/plugins/tasklist/tasklist.php
--- a/plugins/tasklist/tasklist.php
+++ b/plugins/tasklist/tasklist.php
@@ -1914,12 +1914,12 @@
         $mbox    = rcube_utils::get_input_value('_mbox', rcube_utils::INPUT_POST);
         $mime_id = rcube_utils::get_input_value('_part', rcube_utils::INPUT_POST);
         $status  = rcube_utils::get_input_value('_status', rcube_utils::INPUT_POST);
+        $comment = rcube_utils::get_input_value('_comment', rcube_utils::INPUT_POST);
         $delete  = intval(rcube_utils::get_input_value('_del', rcube_utils::INPUT_POST));
         $noreply = intval(rcube_utils::get_input_value('_noreply', rcube_utils::INPUT_POST)) || $status == 'needs-action';
 
         $error_msg = $this->gettext('errorimportingtask');
         $success   = false;
-        $delegate = null;
 
         if ($status == 'delegated') {
             $delegates = rcube_mime::decode_address_list(rcube_utils::get_input_value('_to', rcube_utils::INPUT_POST, true), 1, false);
@@ -1937,15 +1937,19 @@
 
             // forward iTip request to delegatee
             if ($delegate) {
-                $rsvpme = intval(rcube_utils::get_input_value('_rsvp', rcube_utils::INPUT_POST));
+                $rsvpme = rcube_utils::get_input_value('_rsvp', rcube_utils::INPUT_POST);
+                $itip   = $this->load_itip();
 
-                $itip = $this->load_itip();
-                if ($itip->delegate_to($task, $delegate, $rsvpme ? true : false)) {
+                $task['comment'] = $comment;
+
+                if ($itip->delegate_to($task, $delegate, !empty($rsvpme))) {
                     $this->rc->output->show_message('tasklist.itipsendsuccess', 'confirmation');
                 }
                 else {
                     $this->rc->output->command('display_message', $this->gettext('itipresponseerror'), 'error');
                 }
+
+                unset($task['comment']);
             }
 
             // find writeable list to store the task
@@ -2142,7 +2146,7 @@
 
         // send iTip reply
         if ($task['_method'] == 'REQUEST' && $organizer && !$noreply && !in_array(strtolower($organizer['email']), $emails) && !$error_msg) {
-            $task['comment'] = rcube_utils::get_input_value('_comment', rcube_utils::INPUT_POST);
+            $task['comment'] = $comment;
             $itip = $this->load_itip();
             $itip->set_sender_email($reply_sender);