And therein lays the problem. I can't come to grips with either side of that fence.
It makes sencs to autocal subtotal and items total if I'm creating an order from a cart. From there on out I guess it's safe to just let people change price/quantity and leave the calculation for subtotal and total up to them instead of doing it for them like we would in the cart.
It's more work, but more flexibility because as you point out, all bets are off in the order when it comes to totals and possible "new math" involved in discounts.