Man, that does not seem right. I've never had any kind of flare up. It's grease in the drip/water pan that is catching on fire? That has never happened to me, but we don't have the exact same unit. I have a smaller 30" without any windows. How does the grease get into the enclosed chip box to come in contact with the electric element? Or was it dripping onto the pellet smoker box?
Masterbuilt is very good about their customer service, and would probably be willing to ship you out a new door under warranty, if you tell them that it started to pop out while you were using it.