I had the same issues with gift cards on my system, using V13. Completely messed my drawer up at the end of the night. A gift card that should have had a zero balance was also being able to be used for an infinite amount of transactions, this was after we did a gift card sale and then voided the sale. It removed the sale but at the end of the night our drawer was short in cash the gift card amount. And then upon showing an employee how a sale would look if a gift card had a zero balance, the transaction went through and worked on an infinite amount even though it originally had just $25 loaded on to it.