Powerboard overload switch melted
You should never, EVER put a space heater (or other high-draw appliance) on a plug strip!! 

Even thought they are rated for a certain amperage or wattage, most are cheaply made and cannot handle the load of a single high-draw appliance. It's not that they will definitely fail, but unfortunately your experience is not at all uncommon.

What happened to yours was likely not a short circuit. That would almost certainly trip a breaker or fuse. It was probably a poor connection inside the plug strip. A poor (high resistance) connection under high load will create a tremendous amount of heat, but will not draw any more current. So a fuse or standard circuit breaker will not see this as a problem. The same thing can happen with a loose plug/receptacle combo. It's all about Ohm's Law.