Never happened to me. What are you using?
browser/os/brand of computer/resolution?
Firefox on Windows. Happens maybe 1 out of 100 pages opened. I think the time it occurred when I took the screenshot I had Javascript disabled but it doesn't affect anything else (apart from the obvious such as smilies, inline quick post, image popups, etc), and I think it's happened at times when JS has been enabled, too.