However, I've also seen instances where you can win more than the jackpot amount in one credit. Afterwards the game has either crashed or froze, deducted the excess(!) or simply carried on as normal.
Yup, we were called over to our £5 Vivid - Raise The Roof - in the arcade once, someone hit the barcode, got a certain feature (I think it was a Triple Chance type one - 3 varying values on the alpha?).
Anyway, he managed to somehow get £5.10 on it, and the machine reset itself, leaving the barcode still on the winline and IIRC no win in the bank. Refunded £5 as we could only refund a maximum of £5 per game, as that is the machines stated payout limit. Chap seemed happy with that