I did say it is confusing!
Suppose you deposit, get a bonus and win some.
At the end of WR you have $100 of bonus chips and $50 of your own real money.
When you carry on playing you are using your real money first and only start converting the bonus chips into withdrawable cash once you start using it for bets.
But you can e-mail them and ask that you be allowed to wager your bonus chips first!
Once they change your account you only need to wager the bonus chips once through and you can withdraw the lot!
My confusion didn't end there though, because my casino balance shows one figure, but the banking screen shows a different figure available to withdraw - which is actually HIGHER!