Playing with this game some, I passed time till an enemy unit got close. Happened to be the other sovereign. Anyway, ordered an attack three squares outside of town. Sov went out two down a road, attacked. I went with autoresolve for a win, sov turned around immediately and moved one square back. He was free to move from then on.
After a couple of turns, moved him back. Stuck again. In this same location there is also a stuck caravan. Related?