I think this is more a Mozilla bug but just a heads up the case other people complain.
periodically, the Mozilla e-mail client refuses to delete messages. It shows up either as absolutely no action when you press the delete key/button or it shows activity but refuses to perform any other action in that mailbox. Sometimes if you switch to another mailbox and then come back to the mailbox you're deleting e-mail message from, the messages deleted when you re-enter the mailbox.
I looked with ethereal and it looks like Mozilla is not sending any imap commands. Hence my assertion that it's a Mozilla problem.
The only reason I mention it here is because something about dovecot seems to trigger the problem more quickly. I was seeing this kind of problem before but only after a week or two of uptime in the browser. Now I'm seeing it in just under a week (I think) I've only seen at once but I will keep track for future reference.
I got to get me a new client...
---eric