Game Mechanics: Gate (Plus a heal to 40%)

[Bigcountry23]

To start with, I do not remember non-named or non 50+ mobs gating, but I'm going to set that aside for the moment (I assume if this mechanic is in, it was well researched).

My concern is that gating also is healing mobs to 30-40% health as well, and I can't find any indication of this being how mobs gating should work anywhere. I spent 15 minutes fighting a Spectral Keeper in TT because he would gate, immediately have 40% health (when he gated at 5%) and come at me again, until I got him down and he would gate again (rinse and repeat).

Is this "as intended"? Can anyone show me where this is documented (my google-fu is normally strong, and the only reference I can find to non-named mobs gating is TOV).