Musepack encoder, Modification to write MPEG Audio Layer 1/2 Options

[S_O]

Hello,
several years ago it was said that changing the MusePack encoder to mp2 output won´t take very long. But AFAIK nobody has ever released a musepack-based mp2-encoder so far.
Because I need a high-quality mp2-encoder (for authoring DVDs) I tried it myself:

I was able to modify the encoder in a way it outputs a 448kbit/s MP1 file, if the bitrate musepack wants to encode is higher, the last subbands are just cut off, otherwise the frame is padded with 0. The problem is now: After just one musepack frame (=three layer1 frames) the bitrate is decreased dramatically: Beginning from band 5 only 2 bits are assigned for each subband, the lower ones also have 8 bits max. It doesn´t matter at what quality I try, it´s the same for thumb to insane.
Otherwise the output file will play fine (very noticeable artifacts because of low effective bitrate (about 200kbps layer1, stereo, 44100khz), but otherwise it seems to work).
Is here anybody familiar with the MusePack encoder able to tell why there is this bitrate drop? I haven´t done anything special, just disabled MS coding, changed the scalefactors, created a function to write MPEG layer1 bitstream and modified the allocate function not to use unsupported quantizers (resolution is increased in that case) and that allocation is limited by maximum bitrate (that´s not causing the problem). That´s it. Unfortunately the source code is not very structured/readable so I don´t see what I´m missing.
Any ideas?

[S_O]

I was able to trace the problem inside "Psychoakustisches_Modell" to the function "PreechoControl", which is changing a global array. After commenting the array-modifying code the bitrate drop is gone, but the bitrate allocation is awful. Most likely this is not the only problem. I can encode decent sounding 448 kbps MP1 file using a fixed allocation table (not using psychoacoustics at all).
What am I missing that the function "Psychoakustisches_Modell" is returning no useable values?