Random Open World Absorb

So I just recently got my death knight to 80 and I've noticed a random absorb affect occurring while leveling. It occurs when you cast a spell on a target while on a flying mount, all of the damage will show up as 'absorbed'.
Which is weird because I do have the 'Auto Dismount in Flight' setting active where it says: 'If enabled, your character will automatically dismount before casting while flying.' The key part being dismount BEFORE casting...

Anyway, I'm just posting this to ask if anyone else has noticed if this is occurring, if so then it's one hell of an annoying bug.