BAPI_SALESORDER_CHANGE is not updating custom fields all time

Hi All,

I'm trying with  BAPI_SALESORDER_CHANGE  to update a custom field in header level but sometime it successfully updating and sometime its not with the same data.

Please suggest.

Here is my code:

*-----Populating structures for 'Valuepart1'
wa_bape_vbak-vbeln = v_salesdocumentin.    " Order Number
wa_bape_vbak-zzkkber = wa_upload-zzkkber. "' TEST'.
wa_bape_vbakx-vbeln = v_salesdocumentin.
wa_bape_vbakx-zzkkber = 'X'.


wa_bapi_extn-structure  = c_bapi_struc.    " c_bapi_struc->'BAPE_VBAK'.
wa_bapix_extn-structure = c_bapi_strucx.   " c_bapi_struc->'BAPE_VBAKX'.
wa_bapi_extn-valuepart1  = wa_bape_vbak.                "#EC
wa_bapix_extn-valuepart1 = wa_bape_vbakx.               "#EC


*-----Appending I_EXTN.
APPEND wa_bapi_extn TO it_extn.
APPEND wa_bapix_extn TO it_extn.

*-----Populating structure K_HEADERX
wa_headerx-updateflag = 'U'.  " c_updt->'U'

*-----Calling BAPI to update Sales Order
CALL FUNCTION 'BAPI_SALESORDER_CHANGE'
EXPORTING
salesdocument    = v_salesdocumentin
*          order_header_in  = wa_header
order_header_inx = wa_headerx
TABLES
return           = it_return_ch
extensionin      = it_extn.

CALL FUNCTION 'BAPI_TRANSACTION_COMMIT'.