Hey manutoo, here's an old bug that used to occur pretty rare but its still there, happened to me today.
So I played against this guy who served only from corners which was really annoying but once I took the 3-0 lead he retired. So right after that I gave him bad reputation and then clicked "Ok" so I can return to the main menu. But as soon as i clicked 'Ok' the game just froze and I couldnt do anything except restart my PC from the button. I tried using CTRL+ALT+DELETE to close the process but for some strange reason my mouse wouldnt appear on the screen. Now, I dont know weather this bug occurs only if you give bad reputation to someone who retired or if you just click 'Ok' after someone retired in the middle of the match but, you should take a look at both cases. This situation is rare because very few people actually retire during a match, but when they do this is what happens.