They have bypassed the skreem somehow because you can only start the car when the skreem gives his ok and send the right code to the ecu. If the skreem don't send the code the car will start and the engine died after a second.
And you don't need any "temporarily" bypass, the ECU asked the code from the skreem when you put the ignition in pos2 no matter whether you continue to turn to the ignition position.
And if the car runs the transponder isn't needed any more, you need it when you starts the engine again. I thing this is a safety thing, so that the engine don't stop when there is a problem to detect a transponder when you drive the car.