I always set with my trigger on the bottom,I also bend them into a rounded---m---.I think if you do this ,you will not run into any problems.
When I set my trap,I make sure that the trigger sits in the middle of the jaws,my guess is,one of the trigger wires was off to the side to far.When your trap was fired,the trigger wire got entangled in the jaw ,and kept the jaws from closing fully.
Tom