Never happened to me before, but I have heard of it. Usually it seems to happen when people turn on their heaters to fast and don't let it get set with the tank before plugging it in. Perhaps just a bad heater. Bet its a pain to clean up.
Yes, it burst. It was not a new heater, I was not moving it around or anything. I just came home and found it like that. The whole thing did not shatter, however there were a couple of pieces of glass that was in the tank that I got out.
Wow you really mean that you came home with the heater in the tank and broken into smaller pieces inside the tank? Did it kill any of the fish? Have you replaced it yet?