I engaged in a battle against some earth elemental army with a Henchman, Maussolos, and some trained units. During the course of the battle, some of my trained units and my henchmen were reduced to zero hit points, though Maussolos pulled through. Imagine my surprise, then, when after the battle I found my remaining army stack (including Maussolos) recuperating in a nearby town, with the Henchman incapacitated.

I was under the impression that if you entered a battle with two or more heroes, and at least one of your heroes survived even if the rest took lethal damage, your stack would not be teleported back to a town to recuperate but would rather remain where they are, with the fallen hero accruing a wound and being reduced to very low hitpoints.

Therefore, this is either a bug, or my understanding of how hero teleport recovery mechanics operate. However, if you get teleported back if even one hero falls in battle, this makes multiple hero stacks even worse than they already are. They're enough of a liability as it is, there's really no need to make them even more of one...