[Boxster986S]

Transmission is electronically controlled. It does not have a mechanical park pawl that drops in place to lock the transmission like older automatics. Therefore it has to rely on other methods to keep the car from rolling when you engage "P" on the gear selector.

I haven't found any documentation, but think the "P" transmission brake is different from the wheel parking brake activated by switch on lower left dash. The "P" transmission brake may be in the transmission itself or on an output shaft. The parking brake on the dash is for the wheels. So two different brake functions entirely, transmission or wheel.

 

[Boxster986S]

DBLXX - where are you located? Maybe your GLA is a different spec than what we are used to.

Most of the people on this board are in the US or Canada. There is no red handle on US spec GLA and I have never seen a warning on screen like you describe.