I don't know for sure, but I guess when the action is closed the front of the extractor is located in position by the receiver. As the action is opened and the bolt rotates, the front of the extractor is still held in position by the receiver.
Then as the bolt is withdrawn the front of the extractor doesn't clear the receiver until the rear end of the extractor has entered the bridge raceway.
Anyway I'm sure Joel or some of our other Mauser guys can tell us how it works.

A beautiful rifle by the way.