Nowadays, most casinos exclude a list of lots from being played with bonus money. This is a direct result of these games having been previously used for bonus abuse, for example when the bonus funds were used to collect items or play through to bonus features, only to be switched with real money when the features would start.
Some of these games include Robin Hood - Shifting Riches, Holmes and the Stolen Stones, Castle Builder and Tomb Raider, to name a few.
Playing these games with bonus money may not be possible, or the games won't contribute to the wagering, which would mean that you just loose the funds. Also, should you manage to turn over the bonus, the casino will check your game-play before initiating a withdrawal, and if they see game-patterns that are not permitted, they will void the winnings.