I solved the issue myself

Have a closer look at this pictures:

( You see that the buttons get pressed by the holder )

THE SOLUTION:

( Just turn the holder 180° and it fits )


( There is even a small slot so the buttons don't get pressed )


Its a very solid and stable car climatic holder for the N900, worth the 10 Euro. Still if you wonder why your buttons get pressed, well just turn it around and don't be dumb like me