Mails in Kontact open grey
 

We use Kontact as a client to Kolab with groupware functionality.
One user gets grey mail when she opens them. In the preview she can read then but when she click on them to open, the window is entirely grey. I tried a few things like going through the settings and deleting the IMAP file although the latter was for a problem she had at the same time where Kontact would crash after a minute or so. It also did seem to solve the problem of not being able to see it even in preview and e-mail appearing as empty entries in the inbox (the subject - sender - arrival line; it became visible as soon as you clicked on such a line)