I ran my one war horse mounted hero, that had two horse mounted units accompanying her, over a loot square. The loot was a wolf mount. It showed in my inventory.

Immediately after picking up this wolf mount, something strange happened to the stack. The interface acted like I had two stacks where ever I moved my hero. When clicking on the arrows to cycle through these two stacks, the name changed on the party but the same units listed. It didn't actually duplicate the units.