I have this problem and found this really annoying too.
Mac OS X 10.9.1
Almost everytime, when I hit the enter key in the address bar.
Sometimes it will,
- bring me to google search even I enter a URL
- show no response, empty page when I enter a URL, or a search token ( I need to go back to the address bar and enter key couple more times to get it work. )
- When I enter search token, it only search part of my token. ( I needed to wait for like 2-3 sec to get it display the dropdown list in order get it runs correctly. Maybe it's better to start giving me search suggestion if I stop entering for like 2-3 second. For speedy search token entered, I DON'T need suggestion since I know what I need to search...)
Fair enough, but that's only valid for the hover effect. Opera's buttons don't change even in their pressed state, which buttons do in e.g. Finder or Safari.
Furthermore I think the reason I find the lack of hover effect jarring in Opera is that its buttons don't really look like buttons in other OS X apps, those are usually outlined and look like well... buttons.
IE, Firefox, Safari, etc - no other browsers seem to have the problem. Opera also doesn't always shut down, and I won't know until I try to run it hours later - I get a 'Opera is still shutting down' message with an option to force it to start. It also bombs fairly often with Yahoo mail.
Dunno what happened - Opera used to be great. Just seems a bit shoddy now.