I found in the battle oob that my cavalry units contains a certain amount of polearm armed heavy infantry who get killed chasing the cavalry around the battlefield... that brings a 1900 day level31 campaign to a halt until fixed. However, this battle also followed a siege battle that went as planned but included putting the cavalry into a shield wall.. (I want my expensive horsemen to use their shields during the siege).. and splitting the heavy infantry (no shield 2hander guys) into a seperate formation. So this needs to be sorted and give some flexibility back without spending ages fiddling with sliders and inadequate option buttons before each battle.