https://youtu.be/rLx9hwsvgYQ
Video from HS north, for anyone who wants to see. 35-36ish minutes in is when I finally am at the teleporter in the back of north to test pet vs. mob vs. fleeing mob.
Izmael's comments have made me think that perhaps I haven't spent enough time with this mechanic to be sure of my conclusions... but it seems pretty suspicious to me that literally the only times I've EVER seen a mob trigger one of these teleporters is when it is fleeing. Small sample size, I suppose. Maybe I'll run a charmed pet back and forth across the central pad in basement 30 times when I log on again and see if it works at all.
But again, regardless of that, why did a mob stepping on a teleporter to a different zone end up teleporting to the zone-in?