I have no way of verifying any gains, the funds are moved backwards and forwards between accounts when you bet and there is no game history stored once the game is over. There is nothing to check aside from a long list of "move" transactions which amount to incoming/outgoing transactions between accounts so trying to figure out if you ever actually had the gains you stated would be a lot more effort than it's worth. You were refunded your original deposit, you should be glad of this.
The display bug is actually a problem with all recent PoS wallets. BitGem, BottleCaps & Cryptogenic Bullion etc. all report strange values for any account aside from the default account on Windows Daemons. The site compensates for this by offsetting the dodgy value to get the actual value but occasionally there is a minor display oddity, perhaps due to the dodgy value fluctuating between the values being compared. I have actually considered just removing all of the PoS coins because of this issue but as it stands it's merely a display issue.