Mount & Blade: Warband

Mount & Blade: Warband

L'Aigle
Artillery switching sides during battle
I have a 124-man party and my faction won't go to war, so I decide to help out Prussia in their war against Poland (without resigning my allegiance to my current liege.) I end up fighting a Polish patrol that attacked a group of Prussian farmers. At the start of the battle, there were 6 notifications that something had gone wrong in the script (e.g %*#$@ Artilley_Faction.) I had two artillery batteries, therefore one notification per artillery AI. I won that battle, and found myself doing the exact same scenario a few minutes later (Polish patrol vs. Prussian farmers.) The same switch happened again, and I ended up losing 3 men to my 'rogue' artilley.
Does anyone know how to fix this? I'd like to know before fighting any more battles.
Many thanks.