Thanks for the acknowledgment, Trivaldi.
Pottburter, I also had that same issue with APU spells vs warbots.. I even had a GM watch me as it happened, too. They could see the numbers @ 400-500 dmg, but not a sliver of health was going down on the warbot.
If you relog you'll see the actual position the mob died at. It's an annoyance, but there's your workaround