Yeah, I'm not really sure exactly how it's supposed to work, either. The way that the background of the targeted harvest flashes back and forth with each click doesn't really intuitively display whether you've queued up another swing or not. It'd be better, I think, if it just changed once (indicating that you've queued a swing), and become unable to change again until you're in the middle of that new swing.

That said, the system is workable. If I just want to harvest quickly, I mash the button. If I want to be careful, I pause between each swing to make sure that I initiate only one additional swing.