I don't understand your issue with emptying your wallet. If you're entering more than you have, it should ask you if you want to send the entire wallet. You can also use Options > Empty wallet to empty your wallet. No need to remember the amount from the main screen.
Last time i tried that it didnt work. It only showed me that i dont have enough coins and how many i miss. At least i could calculate it with that value. I didnt know the option, i will test it. And ill check out if it still works what you said. It worked before, yes, but this question doesnt pop up anymore. At least thats what i found last time.