Threads don't stay "read"

[Hydrox]

Everytime I mark a thread "read", after closing browser and visiting forums again it's again bold, like I've never read that. I've tried using marking all threads "read", but still that happens. Makes thread tracking hard.

 

I'm using Firefox and browser is set up to accept cookies. Also site logs me off usually within minute or so. Probably as I'm typing this I get logged off again.