If that is the case, then it most likely occurred after we moved from phpbb to vBulletin. Simple option to fix it, select all messages in a given page by checking the checkbox right next to message number:
After that, scroll down to the end of message list and from the drop down menu choose mark as read and then click on go.
You most likely need to perform this at the last two pages of your message list. In case it still shows that, you will need to do this on sent message list, though it is highly unlikely it would be needed.
The reason I told you to refresh page was because I had run maintenance tool to repair user profiles after seeing your post.
