It happened to me something alike: last week I was playing around in one of the dice BTC sites, and then there was this bug that out of nothing multiplied my balance to way more than 1 BTC (when, at first, I had only the free faucet initial credit).

I informed the admins and they fixed it instantly. They gave me a reward of about 10% of the bug credit. (moments after, I lost the reward gambling there  )