Hello,
I just checked today on your account BramVB.
You had 2 unread topics on the forum “Numista website”. One of them was a recent topic, which you probably didn't read yet, and the other was an old topic. A spammer posted on that old topic a few days ago, hence marking the topic as non-read. When the spam message was deleted, the topic was still flagged as non-read. This is the current normal behaviour, although I agree it's not ideal.
Clicking the button “All read” sets back the count of unread messages to 0.