I know I would unplug any damaged heaters before removing them, but I've seen electrical damage first hand. To be fair though there was a massive heater recall a few years ago because they were dramatically failing, but I can't remember which line they were.
Marineland Stealth and Stealth Pro Heaters were recalled in 2011.
http://www.cpsc.gov/en/Recalls/2011...Pet-Group-Due-to-Fire-and-Laceration-Hazards/
In this case though, I'm also guessing this was a case of user error.