Hello - yesterday, I looked at my Tour and all of the contents of my Messages folder were gone! This includes BES/Exchange and BIS/IMAP messages. I didn't lose anything else - still had SMS, call log, etc. I have a ton of free memory available, so it doesn't appear to have been a memory shortage. Since then, messages have been syncing and staying perfectly.
Has anyone else had this happen, either on the Tour or on another BB? Thanks!