I'm not the only one who has experienced this, a few others mentioned it too. During the Anniversary Bash, a small black dot appeared in front of my character, and stayed there for a while until the game was finished. Later on, the same thing happened, but the black dot had grown huge and was covering about half my screen.

In all my years of online playing, i've never seen such thing before. It's not really a big problem since i probably won't be seeing it again, but i've been wondering: do any of you have an idea what can have caused this? If it was lag, then it must have been a very weird kind of lag ;-P

what have you been doing all these years

yeah it happens, mostly lag. im not positive the cause though.

It should go away when you rejoin though. It happened to me too, but there was something weird going on because the game suddenly ended (I didn't get a "you won\lost" screen).

When the level ends, the screen turns black (except for the readouts and your rabbit), starting with the center, and growing in a circle. Sometimes, due to lag, part of the circle will stay. Especially when two levels are ended in quick sucession.