I have a light bulb pop out from time to time from the spot lights or other wedge sockets. The same thing can happen if a small rubber ring breaks somewhere. It's generally a good idea to stop play immediately if you see it happen to prevent the bulb or other foreign object from ending up in the trough, like you had happen, which is where mine ends up most times. You can usually catch it somewhere on the playfield if you stop quickly. Just my experience.