Yep, its been happening with Opera for a while now. Both 9.10 and 9.20 (not sure about <9), I debated making a thread about it. It only happens if you do something specific, give me a bit and I'll figure out how to make it happen.
Edit: Here is what is happening. If the mouse hovers over Pricewatch, OS Resources or TS Extra at the top of the page, their menu's don't appear below them as they should, they instead show up in the top left. They move the correct distance to the right if you go from left to right across those words, its just drawn in the wrong place. They also don't disappear when you aren't over them anymore.