I just had this happen but to the AI.I sent out one unit of campanian cavalry to scout towards the cathaginian city on sicily,after breaking my treaty with them,and was given a force back by a full stack during their turn.They followed up with another attack and i figured my horse were toast as they had several units of elephants,cavalry,spearmen,a seven or eight star general,and various sundries.I was going to hit auto resolve but figured i would tough it out.

I ran my horse around like crazy and at the end of the battle i had one casualty to none for them and i figured it a draw or defeat.Result screen popped up and said it was a close victory?!?

Come my turn the entire army was gone and i could swear the battle took place in their territory though maybe it was along the border of the two regions,.I thought it really cheesy but it was a break after having fought several massive,and bloody,battles in southern gaul and the army in sicily being newly recruited,and green,didn't have to face it.