I want you to know that i have the same problems here.
I guess Roundcube is not functioning as it should be. At least not on my Debian system. I have read others have problems too.
I like the GUI of Roundcube, but that is the only possitive thing i can say about it at the moment.
In case of future updates: maybe it is a good idea to mention the date of the Roundcube package at http://www.ispconfig.org/downloads.htm
When that info is available we know if it is updated or not (yet).
(Same as for Uebimiau).