Roundcube 1.2.3 + libcalendaring, kolab/calendar, kolab/tasklist (all from git 27.12.2016) using MySQL driver

problem 1:

1. Select a tasklist and choose Edit option
2. Select "Send notifications" and pres Save
3. Message saying "Saving data" appears in a right-down corner of the window and it stays there for very long time (few minutes). It disappears eventually, but whole roundcube is freezed (I can't switch between Tasks/Email/Calendar). I can't even log out. Apparently option "Send notifications" is saved in the database.

No error in the log.

problem 2:
In previous steps I added "Send notifications" option to the tasklist.
I now close whole browser (roundcube was freezed) and login again to roundcube

1. Select tasklist from the list and choose Edit
2. Unselect "Send notifications" option and Save
3. This time "Failed to save data" error is displayed. Change is not saved in database.

Error log shows:

[01-Jan-2017 09:21:26 +0100]: <92fod4fa> DB Error: [1048] Column 'color' cannot be null (SQL Query: UPDATE tasklists

SET   name='lista2', color=NULL, showalarms='0'
WHERE tasklist_id='5'
AND   user_id='2') in /pathtoroundcube/program/lib/Roundcube/rcube_db.php on line 539 (POST /?_task=tasks&_action=tasklist)