Activated chainaxe attacks don’t count as backstabs for Pious Cut Throat, which is supposed to refund ult cooldown by 20% on backstab kill. They also don’t seem to receive the backstab bonus from Shroudfield.
I’m pretty sure this is a bug because chainaxe light attacks are also multi-hit shredding attacks and they work normally with all of the above.
I didn’t check chainsword or enviscerator but they might have the same bug.