Well thats the point, I was using up a set of balls I don't usually use. I had more balls in my inventory but I wasn't planning on purchasing any more of these balls.
Of course I saw the warning about it being my last ball of ths type, I just didn't want to buy any more. I had spent money on other balls but couldn't use them.
Seems silly I have to be afraid of using up my last ball of one type during a round just in case it gets taken out of play.