When silver ball specific autobuy is on, the discount upgrade will glitch back to full price occasionally, effectively destroying your ball's value.
+1 this is a really frustrating bug. Only way to revert it is to exchange for gold to reset silver. Also to add, it's not just on autobuy, it happens often just by clicking buy. If it helps narrow down the bug, every time it happens it doesnt fully reset if you are low enough, it goes up by 10x. So for example if I'm at 10% discount and I buy one more, rather than going down to 9% it goes to 90%. Or from 6 to 5 it goes up to 50%.