Hi there,
(I searched for similar issues in the archives and found nothing matching, so here we go..)
I was giving Roundcube (anonymous CVS from today) a spin and accidentally noticed the behaviour specified in the subject.
If you left-click on the Inbox folder while pressing either the Ctrl or the Shift key a new window opens up (well, depending on the browser configuration) and the session becomes expired.
This is on a clean, updated Debian Sarge system on today's anonymous cvs (server), while using Firefox 1.0.7 (client).
hth, Michele