[General Tacticus]

Strange. Ulm's crossbowmen are tough enough to take on light infantry in melee if need be, and their knights shouldn't rout that easily...

What is sure, however, is that Ulm's crossbows (arbalests, actually) are very, very powerful, and can easily kill their own knights with friendly fire. Which can cause the knights to rout.

I think you got a very unlucky stretch of failed moral rolls, that's the only explanation I can think of...