Mine happens when I change computer. I click unread posts on my laptop of phone, and then when I go to the main computer, and click it again it will say I have none, which is when the 'all unread topics' button works ![Wink ;)](https://www.playmofriends.com/forum/Smileys/classic/wink.gif)
Thats exactly what I mean Damo, When yoo are on device x, basically when you click "show unread posts" it loads all those topics in the cach of that device, The board system will then erase them from your "not yet read" posts list, it will however keep it in the cache of your device. When you switch to a different device your queue of unread posts is empty (but stored in the cache of the other device).
Same holds true for Topics with unread threads btw. If you click home, you will see marked which topics have unread threads. When you enter a topic and then leave again it will not show up in colour anymore eventhough there are still many "new" threads. It basically assumes you have read them all and will only highlite again when a new posts is made to one of the threads in the topic.
I hoped I managed to explain myself adequately.
I have no clue about your messages though :-(