The UDH hanger is held by a torqued centre section. A force ( invariably a hit to the front of the derailleur) strong e nough to overcome that torque enable the UDH to rotate about 60 degrees. Any further rotation should be prevented by a "stop" on the dropout. From the damage that has been reported here it is a failure by Trek to make a stop on the drop out strong enough to prevent the hanger rotating further than it is designed to do if hit from the front..............nothing to do with what material the main part ( other than the bolted centre) of the UDH is made of. It is questionable whether a UDH should be used on carbon chain stays in my opinion for that reason.