Due to the bug [@Shienvien] reported above, I rolled back the server to the state it was in right before I implemented the unread-post system. Some other minor changes were also rolled back (collateral damage).

Couldn't figure out the issue in 30 minutes, so I'll dig in this weekend. Makes me want to punch some pillows. :lol

Let me know if it's still an issue. So far it seems to've gone away.