This is a known issue. It has been repaired a few times only for the issue to resurface. There is a fix in the works but I'm told it's waiting on some additional hardware.
In the meantime you should be able to use the My Recent Topics drop-down menu, located on the red navbar, to track all posts that you participated in.
Originally Posted by Conrad
Happening again. Seems like it happens most in Appearance and Detailing