I experience the same issue since a month ago or so, on 3 computers, with Win7 and Win8.1 as well. After a longer period of time and lots of opened tabs, I simply cannot write to any text box on any tab, I also cannot refresh the page with F5, or search with F3 buttons, and the mouse gestures stop working as well. I tried to close as much page as possible, but it seems that only a restart of the Opera helps. There's no suspicious CPU over load, nor memory overload issue, and the only extension installed is AdBlock with CatBlock ( 
). Actually I tried to close the tab and reopen it, but Ctrl+W also not works. How can I help to solve this issue as it gets a bit uncomfortable for me? Thank you!
Edit: as a remark, Ctrl+click to open link in a new tab still works!