Normally, the Message List contains a list of messages and deleting
the current message will shorten the list by one entry.  Occasionally,
however, the entire list goes blank.  Kmail recovers if I select a
different folder and then return to the original folder.

In article <20131204052834.14616.81510.reportbug@localhost> you wrote:

I've seen this behavior in imap folders that contain server side hooks in
dovecot (that is, the antispam plugin), specially in the Unsure folder, which
always contains a small number of messages, I thought it was related to
hook timing, as it seems to be executed before sending the imap reply.

But it might be something completly different. Please let us know about your
setup, also, this is an upstream bug, and it's already reported there.
I'm marking this bug as such, let's continue the debugging there.

Thanks,