Before closing Opera, try ctrl-left-clicking the currently-selected message in the list so that there are no selected messages. On startup and opening of the view, Opera should then select the top-most or bottom-most message (depending on your sorting settings).
If that doesn't work, do that again but also switch to a different view before closing Opera.
The trick should work. However, once new messages are fetched after startup and focusing the top-most message, the selected message will be one below the first newly-received message.