I've clicked on the 2 koban button to collect from harem so many times, it's pitiful. It's usually when I'm sleepy, so it's my fault, but there isn't any confirmation what-so-ever unless you are refilling stamina. And that's only when you run out and you click the button once more and the game asks you to refill it. Otherwise there is no confirmation for anything else. You spend the kobans as quick as you spend the in game currency.