BAPI_TRADINGCONTRACT_CHANGE won't delete partner functions

[ccorby]

Provided is an abridged version of my code that hopefully conveys how I am utilizing it. ls_hdr and ls_hdrx remain empty, and both bapis return with sy-subrc = 0.

DATA: im_updkz TYPE updkz,
        ls_hdr TYPE bapitcheadc,
        ls_hdrx TYPE bapitcheadcx,
        lt_partner_changes TYPE TABLE OF bapiparnrc,
        lt_return TYPE TABLE OF bapiret2,
        lt_return2 LIKE bapiret2.
im_updkz = 'D'.
APPEND VALUE #( document = wa_assoc_asso_tab-bas_docnr_rec
itm_number = wa_assoc_asso_tab-bas_item_rec
partn_role = 'WL'
updateflag = im_updkz
p_numb_old = p_numb_old
address = wa_wl_tab-adrnr ) TO lt_partner_changes.

APPEND VALUE #( document = wa_assoc_asso_tab-bas_docnr_rec
itm_number = wa_assoc_asso_tab-bas_item_rec
partn_role = 'LF'
updateflag = im_updkz
p_numb_old = p_numb_old
address = wa_wl_tab-adrnr ) TO lt_partner_changes.  

  CALL FUNCTION 'BAPI_TRADINGCONTRACT_CHANGE'
       EXPORTING
               TRADINGCONTRACTNO          = wa_assoc_asso_tab-bas_docnr_rec
               HEADDATAIN                 = ls_hdr
               HEADDATAINX                = ls_hdrx
             TABLES
               PARTNERCHANGES             = lt_partner_changes
               BUSPARTYIN                 = lt_bpin
               BUSPARTYINX                = lt_bpinx
               RETURN                     = lt_return.
  CALL FUNCTION 'BAPI_TRANSACTION_COMMIT'
         EXPORTING
           WAIT          = 'X'
         IMPORTING
           RETURN        = lt_return2.

The return table for bapi_transaction_commit is all 0s, while the return table for bapi_tradingcontract_change contains a single row with the following:
type = S
ID = WB2B

Number = 005

Message = Trading contract is saved

log_msg_no = 000000

message_v1 = trading contract #

parameter = 000000

row = 0