I had similar things - I scored a marginal victory at Montebello (60.000 Frenchies of mine left, against 45.000 Allied), yet I wanted to continue to mop everything up, as I had a nice "hockeystick" setup of my Army in the valley, with the curved part in the south ready to flank and destroy the Allied center.
This curved part consisted of several corps, who did not at all respond to my deployment orders. Closer inspection revealed that the regiments were "attacking units" but there were no enemy units in the vicinity (they were more up north, about >2.000m).
To my dismay, my army reduced to 50.000 because the flanking manoever never happened, and the battle outcome became indecisive.
This was all in conscript mode, as I am learning the ropes - I thought maybe I was doing something wrong, but reading the previous posts, it might be some sort of bug. Or maybe I still am doing something wrong