New post notification count isn't correct when user deleted his own post and didn't refresh the thread

[c933103]

Step to reproduce

1. Reply in a thread you previously replied to
2. Deleted the reply you just make
3. Go to other threads without refreshing the thread
4. Let someone reply to your previous post, and not other replies
5. The new post count for the thread in threadwatchlist will now say the thread have 0 new post but is in red, indicating there's a new post mentioning your post