user config settings in roundcube

[JP Horst]

Dear List,

in my kolab3.1 installation (CentOS) I have one user, for which I tried to change the update interval  in roundcubemail under Settings/preferences/User Interface.

However after logging out and back in, the update interval is always changed back to 1 minute, likewise the date format cannot be changed. With other users this problem does not occur.
Under Web-Admin / User Administration I can see no configuration differences.

Does someone know, where to correct this problem?

Kind regards,
Jens