Team, I have a layout in Quotes with Products to estimate the budget

The thing here is that I've added Discounts to the grand-total (that works fine) and also possible per line. This one does not work: everytime i choose a product, and select the price from pricebooks, the discount field inline only works for direct discount but not with a percenteage. It lets you to input the % to discount but nothing happens. 

Could you help me please?

PS: I don't have anything in Unit Price in Product Module, just PriceBooks.