The bike backfires, usually at startup and the pressure generated in the airbox blows it apart. Some say that fuel in the airbox which can get deposited there a few ways aids in the explosion in some cases. Another thing thats been mentioned is that if your airbox is modded, IE:snorkels removed, bottom drilled, aftermarket filter, that it's less likely to happen because the lesser restriction doesn't allow the pressure from the backfire to build up faster than it can escape.
