Ah, there's your problem then. Town Portal routine clears all nearby enemies and then stops combat completely. If the goblins were too far away it wouldn't attack them, and then after you're back in town trinity has no memory of what was where, so it wouldn't remember to chase the goblins.
Really it was most likely just bad luck. It won't happen very often at all, but do let me know if you see it happening again.






