Excellent work on this, Scat and Night! I'm excited to see that your diligence pursuing this phenomenon has paid off!
From the "behind the scenes" extras that Bungie has released over the years which show the various iterations of the Halo game engine, it's clear that the system for managing in-game objects is incredibly complex. For instance, there is an entire layer of processing which analyzes which objects may possibly be affected by events such as explosions and weapon firing. This is done so that time can be saved avoiding updates to objects "out of scope" of the event.
I'd like to think that this is some manner of respawning behavior; perhaps where these objects (elites, cops) are being despawned and respawned by the "lethal damage" of the grenade explosion and it is manifesting in a bizarre way due to the fact that the objects have a special flag, being that they are "dead" versions of objects which would normally have AI characteristics.
This doesn't explain (at least not well-enough for me) why a respawned object would change its orientation (e.g. animate itself to stand up to perhaps a default spawning position) rather than disappear/reappear like we normally see.
So I am left wondering if we have any other in-game evidence of similar objects (not doors) animating to change their orientation and right themselves after being disturbed by the player.
Well-wishes to everyone, and Long Live the SGP!