Perhaps, you lost your check in Enable Advanced Keyboard Shortcuts. Go to Settings (Alt P), and then under Shortcuts, put a check in Enable Advanced Keyboard Shortcuts.
If the Check is already in it, then take it out, close Opera, open Opera. Then put it back and see if that makes a difference.
Perhaps,if that doesn't work try an extension, like Opera's Simple Undo Close.
It supposedly supports keyboard shortcuts. There are other extensions that open the last tab.
That is so weird! I go to "About" to make it check for updates every day. It says i use the latest version...
However i checked on opera's site now, and you're right about that. 19 is the latest...
could you also post a link to where i should make the suggestion? i kinda bet that it won't be implemented on 19 either.. I'm downloading 19 atm btw