Just bumped into this today, when I upgraded to a testing package in Fedora:

https://admin.fedoraproject.org/updates/FEDORA-2014-2672/dovecot-2.2.12-1.fc...

For details, see this bug:

https://bugzilla.redhat.com/show_bug.cgi?id=1066709

Haven't seen this kind of thing before. Sure, it worked the second time I tried to move the message to another folder (I'm guessing index got rebuilt or something), but still, looks suspicious.

Anyway, I'm using mbox format mailboxes, if it matters. Client was Gnome Evolution 3.10.4.

-- Bojan