Something I’ve noticed recently- the banner ads at the bottom invisibly overlap the “Submit Post”, “Submit New Thread” or “Preview Post” buttons at the bottom of the screen.
In other words, no visible part of the ad overlaps the buttons, but if you click on them without scrolling up a little, you end up triggering the ad, not submitting your post.
This is just poor design and not a little bit chintzy and lame.