I think jills is on the right track. It looks like there are burn marks on the filament housing. That would seem to indicate improper distribution of heat. Maybe a flaw in the glass causing the filament housing to shatter from the excessive heat buildup, or more likely a flaw in the circuitry of the filament. Probably just a factory defect. There is always going to be one device out of every so many thousands on any production line that comes out defective. Even with a Quality Control department checking there will still be some defects that are not apparent until after a certain amount of use.
I think jills is on the right track. It looks like there are burn marks on the filament housing. That would seem to indicate improper distribution of heat. Maybe a flaw in the glass causing the filament housing to shatter from the excessive heat buildup, or more likely a flaw in the circuitry of the filament. Probably just a factory defect. There is always going to be one device out of every so many thousands on any production line that comes out defective. Even with a Quality Control department checking there will still be some defects that are not apparent until after a certain amount of use.