While at KSDF loading the PMDG 777F for UPS had completed at Gate B Ramp 109. The tug attached normally, when they started to push the aircraft swung violently into the building. Then the tug was pushing the plane forward underneath the fuselage. The tug then did a 180 degree spin, letting go of the aircraft and with the brakes on the aircraft continued into the opposite building crashing. This has never happened before, and I'll try to reproduce it. I don't know who this belongs to (bug if you will) PMDG, GSX, or P3D. I did manage a screenshot before we hit the building. Is there a log or something that GSX produces that would help put a finger on this?