Why does auto-updating prices reset the discount?

Here is something for the next version of plugin. To get current prices on the products you need to keep automatic price updates on, but, having it on also resets any discounts that you have manually assigned to any products (that is by adjusting Product price and Sale Price). Why not have a box where you select if you want to update the product price field automatically or not - this would keep the discount sign for x% (or a slightly updated percentage)? Right now it's always reset to zero if the supplier hasn't bothered to fill in a discount.

It would be simple to implement and wouldn't mess up manually assigned discounts.