I remember once, about a year and a half ago, one other customer reported a similar issue. Obviously, that was a concern to us, so we tried to recreate that condition here at the factory, and what we found was that if the wrong wattage of bulb were installed (the customer had replaced their original bulbs with newer, higher wattage bulbs this could occur, but only after the lights were left on for an extended period of time. We got the correct wattage bulbs put back in and also discovered that the light shrough actually had some play (room) to be moved down a little without having to drill a new hole - so that put the lights even further from the ceiling panel and all was well. The discoloration on the ceiling panel was cleaned off using some heavy duty cleaner.
FYI
ST