I had that problem as well, except it was with the Swedes. I did all the Montebello OOB's and map. Gave the French their marching orders and then fought the rest of the battle as the Coalition. I left everything in initial setup as it was my first battle. Those Swedes never moved an inch until the French punched a massive hole in my lines, then they decided it was time to march to where I had initially wanted them. Of course they got shot to pieces and ran off.
Also, I had this happen with the cannons for the French. I had the same setup as the battle I stated above but this time I put the Coalition on the defensive. Well the Coalition killed everything I threw at it so I fell back to that town where Napoleon was. So I withdrew my forces as the Coalition still had three relatively intact corps and I had one. I put the Coalition on pursuit to see how things would work out. Well, what was left of my army withdrew in good order. This is, I mean, all the infantry withdrew as the cannon stayed behind (delaying action?) and preceded to route the pursuing Coalition forces for the loss of about 9 guns all together.
Weird stuff imo. I lose a battle that I thought I could have won if a certain group of guys put one foot in front of the other. I then win one when I could have easily lost when an entire branch of my army decides they'd rather stay and fight the entire Coalition army. Go figure
PS. How the heck do you take a screenshot? I've tried "P" "Ctrl+P" and "Print Screen" but couldn't find the pics.