Westcott Light explosion

Hello

About six months ago I purchased a Westoctt light kit with two softboxes and a stand up light. The softbox light bulbs are 500W and the stand up light is 100W Today one of my softboxes made a popping noise and then smoke came out. I unplugged the thing and the whole bulb inside shattered leaving the bottom intact inside the softbox. Is there something wrong with my softbox? I cant' figure out what would cause this. I never plug it into a surge strip nor do I leave it on long periods of time.

thanks

Bryce