Posts/Threads really late or incorrect dates?

I don't know if my brain is fried, but often (like today) I check in with the Forum and there are suddenly all these "new" posts. But I usually check the Forum once per day and there is nothing for days on end, then suddenly Bam! a whole heap.
And when I read the posts they are dated around two weeks ago or something. Sometimes I remember replying to something and it appears on the thread, but then it appears as a "new" post when it's been done ages ago.

Can anyone shed light on this?