Seems like the latest version of thunderbird email client is deleting messages off the server - even unread ones. If you back out of the program and go back in, your new messages are gone. Is there a fix? I have ensured the settings state, leave messages on server until I delete them. Is this a known bug?

Go back to version 1.0.6
Yours is only a Release Candidate, which is still not finished!

I realised this bug on occurs if you mess with the settings. Fortunately I still had a copy on my other computer. I fixed the problem by using mozilla/thunderbird/firefox restore program. I saved the settings on my laptop for thunderbird on my flash drive, then transferred it over to my desktop. Thunderbird now works as normal on my desktop, but won't dinker with the settings anymore - apparantly the release candidate has this bug...

I also noticed all my messages which I thought were deleted off the server suddenly magically reappeared!