(IANAL) BSD-style licenses generally only require that the file and its derivatives retain the original authors copyright notice. Distributing it under a different license still allows you to fill the original requirements, so there's no conflict there. Or from a different angle, what exactly is the difference between including a BSD file in a GPL file vs including a BSD file in an empty file and then licensing the result as GPL?

Edit: Does it help if I tell you that more precisely they aren't relicensing the file but merely stacking licenses on the file? The process is purely additive.