Hello Shai,
thank you very much for your reply. I can ensure there is no missing COMMIT WORK AND WAIT.
After the line 321 is executed, the update function module is called which update database table B.
Since this behavior( table A is updated in normal work process, and table B is updated in update work process ) is implemented in SAP standard function module CMS_LO_DOC_MAINTAIN, for me I don't know why the original design of SAP did not choose to put both table into the same update task.
Best regards,
Jerry