Worshipper – “Ship” [Campaign 2, Mission 4]

I encountered a problem in the last castle. I accidentally stepped on a hedge with my dogs, and they got tangled in it and wouldn't let go, no matter what I did. I waited, defended, and even destroyed the castle with an earthquake, but the dogs were still stuck and were being cut down one by one, about 10-15 at a time. In desperation, I set the dogs to auto-battle, and a miracle happened – they were released! What did the computer do that I couldn't?