Currently, when my pet performs a Kill Command on a mob, that mob will perform it's own Kill Command back at it's target. I say it's target because I received the reflected Kill Command as the mob had me as it's target and my boar Grar performed a Kill Command on it. I tried this with two different pets: Gahiji, a lvl 70 sabre cat that I tamed out in Skettis about an hour ago on the Test Realm, and Grar, a lvl 70 plagued swine that I've had since 60 on the live realms. Gahiji is at loyalty level 1 and Grar is at loyalty level 6. Gahiji knows no other skills except growl, and Grar knows Charge, Gore, Bite and Growl.

I was able to recreate this bug every time I used the Kill Command.