Another maybe issue, or maybe just the way the forms work:
Posts Owed seems to show ANY bookmarked thread that has activity after your last-dated post, regardless if you have looked at the thread to clear the 'new activity' flag.
Clarification:
It's only really an issue if, for example, you have a group game OOC thread bookmarked. Lots of chatter, it shows up in your 'posts owed' tagset, even if you've looked and seen that it doesn't require a response from you.