[Yaiba]

Yeah, that fixed it. Do you know why it occurs?

No not really it happens on other forums than this one I can tell you that

Sounds like a MyBB or plugin issue, then. I've seen this once and I've been unable to replicate it, but I'm trying to write some kind of debug script.
Do you know of any pages where this happens consistently?

Not really I don't relly remember specific pages it's more like threads not like the home page