Version:            (using KDE 4.1.3)
OS:                Linux
Installed from:    Ubuntu Packages

I am using:
Kubuntu intrepid ibex (8.10)
KDE Version: 4.1.3
KMail Version 1.10.3
Account: Disconnected IMAP

I was trying to solve another problem (http://bugs.kde.org/show_bug.cgi?id=55838)
 by rebuilding the index of the my inbox. I went offline for this, as I didn't want to affect the mails on the server. 
However, rebuilding the index raised the problem of missing dates for more than half of the 4000+ messages in the folder. The dates appeared again when selecting the messages, but you do not want to do this for 2000 messages. So I tried again, this time online. Same problem. Then I chose to fetch e-mail in the hope it would synchronize the problem away, getting the dates from the server. Suddenly there are only about 1700 mails in the folder anymore. Bad! I check my webmail interface whether this has affected the server side, but it is worse: only 109 messages left my inbox. BAD!! Switching back to kmail I see it synchronizing again, resulting in the 109 messages replacing the 1700. Fuck! Four years of mail archive lost, even though I thought having a local copy (Disconnected IMAP) and the mails on the server would protect me from such a loss.
By the way, this is not the first time I lost emails using kmail. It happened to me some years ago, in a somewhat similar way and I stopped using kmail. But I was lured by the shiny interface and nice integration into believing this would not happen again with an up-to-date version.

To sum up: I can not continue to use kmail as long as I want to keep my mails! I am sorry to say this, as I know that a lot of work has been done by the developers. But an unreliable mail client that loses your mails is as bad as it gets. 

Regards,
Felix