I have noticed this happening in my games as well especially if Bonaparte is in the stack. In fact i have never been able to get Him to aid in an attack and when I use Him to attack no other forces in the stack will move in with him

Is there any way to edit the reinforcements in this game? I've been working on a Marengo scenario and have discovered that the editor does not allow for the possibility of delaying reinforcements. 
What about being able to add new unit types such as horse artillery?