I had a strange battle the other day. As the Russians, I was besieging the Mongol citadel of Acre. The siege had just started, and a number of my engines had been set alight by towers. Then, all of a sudden, the game decided I had "lost" the battle, the battle loss narration began ( we put up a good fight, but were were ultimately no match for our enemies blah blah blah), and it ended the battle as a "close defeat" for me. I lost nothing but a few siege engines, there is no battle time limit, and I was not routed from the field. I told no one to withdraw. So why the hell did it make me lose?
I doubt this has any effect, but my commanding general was some minor family member, and the Mongol general was that famous son of Genghis Khan, Ogedei, who had crazy stats like max dread, max command, etc etc.