Yep, I have just seen this last night but it was with the "Dane's". I got ex-com by Pope and Dane's/Hungry join crusade against "Trousels" I started to build forts along the mountain passes and bridges to block the "Hung's" and slow them down so they would loose guys to desertion and the Dane's just sat up by "Hamburg" not moving. I was invading the Dane's I had 3 full stacks hanging around getting ready to wack them they never moved and no one deserted or joined them. I waited about 3 or 4 turns Pope died ex-com lifted so I crushed them and the Hung's.....and got ex-comed the next 2 turns by my own Pope for doing it . BUT "yea" they never lost a guy to desertion? Maybe the AI dose not have that problem???