... just to close this discussion: the problem is solved, it was some dovecot installation error.
No one knows where it comes from really, seems to be a bug in the new version (or package)...
essentially following the suggestions from http://comments.gmane.org/gmane.mail.imap.dovecot/50792 (i.e., creating symlinks into /usr/lib/ for the affected shared libraries) solves it :-)
-- Chris _______________________________________________ List info: http://lists.roundcube.net/dev/ BT/aba52c80