After winning a battle, I've found occasionally found troops from the army in the same province, but no longer in a squad under their previous commander. The battles were won, no commanders were lost or retreated.
I've also not noticed this and moved the commander on without all his troops. That's annoying.
Just occured to me: Is this new behavior for troops that route, but don't leave the field before the battle ends? If so, I don't like it. It adds micromanagement for no real effect. You just have to remember to check Army Setup in each province with a battle.
No, it existed in Doms 2. If troops rout of the field, then they end up detatched from the commander (in Doms 2, they'd usually end up in a different province).
With the new leadership stuff in doms 3, you'll probably see this a little more often than your used to (well, unless your Ermor )