Bug while pricing items in currency exchange

It has happened a couple of times to me now that when i set a price on the i want tab, and after that i click on the tab to set the "i have" price, it just turns the i want price to the current selling price even i want to set it more expensive or it just keeps the current price and overwrite my amount after that and creates a stupid price which i have to correct after, please fix this because its so annoying.