Problems with read/unread mail on IMAP server

[ Edited by Apple Discussions Moderator; Please start a new topic about your technical issue. ]

I'm having the strangest problem and I've yet to find a pattern or explanation for it. I retrieve all my mail from an IMAP server and store cached copies on my Mac. Sometimes after I've read a message, and Mail.app marks it as such, it will re-flag itself as unread after a number of minutes. Sometimes it's immediately, other times it's after several hours. It doesn't happen on all messages, just some, and seems to happen in at random in any of my IMAP folders. It's incredibly annoying. Has anyone else had this happen or do you know how to fix it? It doesn't seem to happen with other MUAs, just Mail.app. Thank you!