>> But according to the quoted literature flap 1 is supposed to open before flap 2.

The quoted literature fits in with the physics of these things. Your car is definitely wrong.

On my E300D, the valve in the crossover opens first, followed by the one in the manifold proper at about 3500 rpm.

Is the rest of the vacuum system "wired" up correctly? On mine, there are quite a few restrictors and tee joints between the vacuum pump and the vacuum supply to the solenoid valves.