Basically what the game reflects (or so i think) is a basic morale rule: If your troops think you don't know what you are doing (i.e. giving them too many attack/fall back-therefore contradictive-orders) they will loose heart (and confidence)and run out on you. I never had this problem, and but I must agree it's sounds like a Bit*h .

Try not using this tactic to excess, and allow them a breather between pursuits, I never use this tactic more than 3/4 times max, after wich I bring the unit to the rear or flank of my main army and allow them a breather...