Recently i faced the same problem in a client trying to update emails via BAPI_BUPA_ADDRESS_CHANGE.
If you are using BAPI, the CRM middleware could doesn’t work because the general data flag for update is expected (in the FM BUPA_OUTBOUND_SET_UPD_FLAG).
To solve this issue try to use also the BAPI_BUPA_CENTRAL_CHANGE before the COMMIT WORK.
Like this example:
CALL FUNCTION 'BUPA_CENTRAL_CHANGE'
EXPORTING
iv_partner = i_partner
iv_x_save = abap_true
TABLES
et_return = it_return.
I hope it helps!