[Alneyan]

Ah, that was it. It happened to me as well, but only the archers routed then (fortunately). They took exactly two arrows for little damage, but routed nonetheless.

You can execute your commander actually; send the offending leader to any province nearby alone, with orders to attack the closest enemy. It should be much better if this province happens to be filled with cavalry, and even gives you a very accurate report of the defenders of this province. Be careful not to let know your other commanders about this unfortunate accident; somehow, it might have an impact on their own morale.