This is very old thread but the answer to this is for any custom enhancement to pricing header/item table, you should extend KOMKAZ or KOMPAZ structure and not KOMK, KOMP or KOMG.
For some requirement it might work directly extending KOMK, KOMP or KOMG but some problem could arise like what the thread starter originally had.
SAP standard program will refer to KOMKAZ,KOMPAZ if it wants to check customer enhanced field changes, not in KOMK/KOMP direct custom append structures.