After debugging it seems T331-NEGAT is unmarked when LTAP-FHUTA (=HU item) is not initial.
Now I have changed my SL02 storage location to HU managed which has as a consequence I can no longer post a goods receipt in MM first (which is our intention in the normal procedure).
This leaves me with the need to do a posting change at the end of the process.
I don't see any way to automate this posting change, because you have to provide HU/SU number via VLMOVE or HU02.
Anyone tried to automate this before?