I want the money to be deducted from the buyers account immidiately.
It's not really an answer, but check the "payment action" (in german it is "Zahlungsvorgang") at the "System->configuration->payment methods" tab. There's a difference between "Authorisation" and other ones.
There's a screenshot:
One of them only reserves the money, but it will not be transmitted ... you should have a look at this.