I was in close contact with AVM the last two days and they did a good and quick job; I had gotten that firmare this morning already but only found time now to test it. It IS fixed :)
So to AVM I need to say: thanks for all the Fritz! And for the rest of you who might still be disappointed about the long time it took from my first report to the fix, one of the remarkable statements from AVM was that because there was no remote execution vulnerability or any danger of information leakage at any time they just planned to fix the DoS condition in the next feature release. Real security threats will still be handled immediatly. Hope the day for proof doesn't come :P