Update: I tested Bitte melde dich an, um diesen Link zu sehen. posted here and it does work on VICE but it does not work on real hardware and also does not work on emulate U2+ drive (with the same behaviour on real hardware).
A pity.. because track1.prg (differently from any other) can successfully load a big 183 block file ($801-BFFF).
Any chance you can make it work on real hardware too?