Tahm Ulti bug

I was playing as tahm, and had only ultied successfully once for and entire game. After trying it a second time, the ulti would cancel as a friend would jump in my mouth and cast my devour on them, but deal the damage to the friend. I t ended up that i got credit for killing my friend while trying to save him with an ulti after a wall jump. the bug happened again, then when i spat him out he took the 10% he had left and died, claiming me the killer.