FINALLY! I wrote this weeks ago, but then couldn't reproduce it, so it's been languishing. At long last I just did in BG1, though I've seen it in BGEE as well, and now I think I know the issue- or have a better hypothesis...
Normally when you see the two ogrillons south of Beregost they are hunched around the dead body of the halfling. Occasionally (it happened 4-5 times in a row between both BGEE and vBG1 back a few weeks) when you arrive at the encounter scene, one of the ogrillons is not near the body but instead on the west side of the trees that line the west side of the road- i.e., totally out of place. In this latest instance Nexlit the Blue Elf was wearing Boots of Speed and proceeded directly to the scene with Inviso, so I was able to catch the ogrillon in the act. This time the same ogrillon actually walking north around the trees to get to that far location. Yet after he got there and paused, he then continued to walk inconsistent rings around that patch of trees, sometimes stopping to the west of them, sometimes to the east, but always counterclockwise around those trees.
I killed him to make sure: it's the special ogrillon that carries the scroll (SCRL3i) intended for Mirianne (MIRIAN.CRE, MIRIAN.DLG). Not sure what the specific ogre .CRE he is though. I had speculated it was a matter of the placement having been too near the trees and forcing a relocation by the game, but I now have the feeling he's got some sort of a wander script on him that keeps him centered on a particular point.
The ogrillon that's in the correct
location every time is at: x=3887, y=1475
The ogrillon that wanders tends to start at this location: x=3858, y=1534
That ogrillon should always stay put hunched around the halfling like his cohort and not wander.