First, the problem. In Opera, the drop-down Reply to the Comment Above goes wonky. The rest of the page doesn't drop down as far, and the Reply part either goes over the top of the next reply (making it hard to see what's going on) or drops behind the rest of the page when replying to the last comment on the page (making it impossible to reply to that specific post without switching to IE or Firefox).
Now, the suggestion. It would be very nice if the option to reply to a specific post in a thread was clearer. I notice a lot of people use the Reply box intended for the original message when they were trying to reply to one of the listed replies.