I've noticed one I haven't seen listed: sometimes, when I write a post, and it's among the first few posts on the current page of the thread, after sending the post, it gets me back to the second last page.
I'm using SeaMonkey 2.8, I've set the forum to display 30 posts/page, and I've noticed this in at least these two
threads (for me, page 2 and page 3, respectively).
EDIT: Add to it that Interplay blast, containing 92 posts at the time of writing, is shown to have three pages in the My Posts list, even though there are four. I guess this has something to do with the fact that news posts aren't displayed at the top of every page now.
I also get sent back a page(or multiple pages...usually no more than 2-3 though) when posting to some threads.