I had a similar problem, I came out of the sewers and the graphics \"smeared\" until I was on the surface, then the ground, everything was black except me and the \"pit\" into the sewers. It was quite disturbing...
And then another time I was walking through the sewers and there was a light blue flash, and I was falling and right in the chat box it said \"You fell off the edge of the world and died.\" That\'s not exactly fair, methinks.