The only thing the casino would have to gain would be OP's original deposit, right?
After the bug occurred, in FortuneJack's point of view, there is no point in fixing his balance until the player decides to withdraw everything. All FortuneJack has to gain is verusfides's deposit, but they have nothing to lose. If verusfides won (like in this case), they could blame the bug, and return only his deposit.
FortuneJack is basically freerolling verusfides - letting them place bets, taking his money if he lost, and not paying out if he won. This is not okay.
I don't know if there was more malice behind this, but if FortuneJack knew verusfides was a plinko player and had a good plinko win coming up from his seed, they might have wanted him to win using "fake balance" to avoid paying out a large win.
Say verusfides never tried to withdraw(that was halted and needed further approval).. continued to play with the 2btc he had won.. loses it all. Stops playing. Would FortuneJack have contacted him that the game he was playing was bugged and caused him to lose his initial deposit and that they would refund it for him.
I bet the answer would be no.