Why ... whhhyyy???

Ok, in the example above I used bmap_process(bitmap1, NULL, mtl)

This somehow fucked the adressing of every other texture up.
For example tex2D(smp, float2(0.56, 0.7)) adressed the last pixel of the bitmap.
Keep in mind, that the externaly used bitmap (through mtlskin1) had the same size.

So now I did that
bmap_process(bitmap1, bitmapSource, mtl)
Again the bitmaps had the same size. AND NOW it works.

I know that the manual states that you have to multiply the adressing of the sourcebitmap with the size ratio.
But this should exclude the adressing of other bitmaps. Especially if they have the SAME SIZE.