Thanks Illori and sorry for my english, nope, it's not what I meant

Trying to explain a bit more :
- There is a section with 10 messages unread (marked with label "new")
- When I click to read the firs one (for ex) but it can be another one with label "new"
- Reading the post go back to the list of topic inside this session and it acts like I have read the 2nd one while it's not true.
- Of course, the real one I have read is marked as read
Doing that with other post make other post as read along with the one I have clicked.
In final for 10 post (unread) reading 4 or 5 post make them all marked as read.
But it's random and sometimes it works like it should : mark only the one I have read and not the other.
I don't know what it happens and from what I suppose and see, it seems to happen to only section where user need to be logged/registered to see that section
The word section is maybe not a correct word, I meant it's a specific part of the forum not visible until we are logged/registered.
Thanks
