This is what is called a "sticky bonus" and is not confined to Internet casinos. When I went to Germany I had to pay 20 Duetchmarks to get in. However if purchased 100 Duetchmarks in chips they gave me a free 20 in sticky chips. A sticky bonus or sticky chip is one that can never be cashed out. However if you bet it and win the winnings are real money. They way to get rid of sticky chips is to keep betting them until you lose them. In the case of Internet casinos you will need to keep cashing out winnings and always leave the sticky bonus in your account, then go back and play again.