Module pool- only first line item data saved, rest disappears??

Question

Hi Experts,
I have one module pool that was developed by other developer. It has header details input fields and items details input by table control.
Now below scenarios occur:
1) When I enter only one line item, and save it, the data is saved properly
2) when I enter more than one item data and save it, it only saves first line item data.
3).When I press ENTER button after every new line item data, it saves all the data properly.
I tried to debug the report but could not find the exact problem statement as the code is written very badly without any comments.
I am pasting the flow logic code below for the screen.
So please help me figure out the problem and solution for it.
+++++++++++++++++++++++++++++++++++
PROCESS BEFORE OUTPUT.
*&SPWIZARD: PBO FLOW LOGIC FOR TABLECONTROL 'IT_MSEG'
   MODULE it_mseg_change_tc_attr.
*&SPWIZARD: MODULE IT_MSEG_CHANGE_COL_ATTR.
   LOOP AT   it_gp
        INTO wa_gp
        WITH CONTROL it_mseg
        CURSOR it_mseg-current_line.
     MODULE it_mseg_get_lines.
*&SPWIZARD:   MODULE IT_MSEG_CHANGE_FIELD_ATTR
   ENDLOOP.
* MODULE STATUS_9001.
   MODULE deactive_screen.
PROCESS AFTER INPUT.
*&SPWIZARD: PAI FLOW LOGIC FOR TABLECONTROL 'IT_MSEG'
   LOOP AT it_gp.
     CHAIN.
       FIELD wa_gp-yposnr.
       FIELD wa_gp-matnr.
       FIELD wa_gp-maktx.
       FIELD wa_gp-meins MODULE check_uom ON INPUT..
*      FIELD WA_GP-DOC_QTY.
*      FIELD WA_GP-REC_QTY.
       FIELD wa_gp-gp_qty.
       FIELD wa_gp-chall_qty.
       FIELD wa_gp-netwr.
       FIELD wa_gp-remarks.
       FIELD wa_gp-exp_ret.
       MODULE it_mseg_modify ON CHAIN-REQUEST.
     ENDCHAIN.
     FIELD wa_gp-chk
       MODULE it_mseg_mark ON REQUEST.
   ENDLOOP.
   MODULE it_mseg_user_command.
*&SPWIZARD: MODULE IT_MSEG_CHANGE_TC_ATTR.
*&SPWIZARD: MODULE IT_MSEG_CHANGE_COL_ATTR.
   MODULE user_command_9001.
+++++++++++++++++++++++++++++++++++
Thanks,
Vishal.

Answer 1

Hi Aruna,
Below is the code as you required.
+++++++++++++++++++++++++++++
MODULE user_command_9001 INPUT.
   ygp_header_mas-ret_type = v_gpt.
   CASE sy-ucomm.
     WHEN 'MBLNR'.
       PERFORM select_mblnr.
     WHEN 'DEL'.
       PERFORM select_delivery.
     WHEN 'INTI'.
       PERFORM grt_gi_details.
     WHEN 'GENT'.
       PERFORM get_ge_details.
     WHEN 'GP'.
       PERFORM get_returnable_gp.
     WHEN 'SAVE'.
       PERFORM gen_gp_number.
       PERFORM gen_data.
       PERFORM save_data.
     WHEN OTHERS.
       PERFORM get_ge_details_other.
       IF it_gp[] IS INITIAL.
         INSERT INITIAL LINE INTO it_gp INDEX 1.
       ENDIF.
   ENDCASE.
   IF v_entry = 07 .
     PERFORM serial_no1.
     PERFORM insert_row.
   ENDIF.
   IF sy-ucomm IS INITIAL.
     PERFORM calc_amt.
   ENDIF.
   CLEAR:sy-ucomm.
ENDMODULE.                    "user_command_9001 INPUT
+++++++++++++++++++++++++++++++
MODULE it_mseg_user_command INPUT.
   ok_code = sy-ucomm.
   PERFORM user_ok_tc USING    'IT_MSEG'
                               'IT_GP'
                               'CHK'
                      CHANGING ok_code.
   sy-ucomm = ok_code.
ENDMODULE.                    "IT_MSEG_USER_COMMAND INPUT
++++++++++++++++++++++++++++++++++
MODULE it_mseg_modify INPUT.
   MODIFY it_gp
     FROM wa_gp
     INDEX it_mseg-current_line.
ENDMODULE.                    "IT_MSEG_MODIFY INPUT    
====> Above module has some problem i think as while debugging it was not updating IT_GP as the current line number was not matching with IT_GP as it has only one line item and WA_GP was changing. Also WA_GP data was getting changed with LOOP with all line items data.
++++++++++++++++++++++++++++++++++++++++++++++
MODULE it_mseg_mark INPUT.
   DATA: g_it_mseg_wa2 LIKE LINE OF it_gp.
   IF it_mseg-line_sel_mode = 1
   AND wa_gp-chk = 'X'.
     LOOP AT it_gp INTO g_it_mseg_wa2
       WHERE chk = 'X'.
       g_it_mseg_wa2-chk = ''.
       MODIFY it_gp
         FROM g_it_mseg_wa2
         TRANSPORTING chk.
     ENDLOOP.
   ENDIF.
   MODIFY it_gp
     FROM wa_gp
     INDEX it_mseg-current_line
     TRANSPORTING chk.
ENDMODULE.                    "IT_MSEG_MARK INPUT
+++++++++++++++++++++++++++++++++++++++++
If I press ENTER after entering each line item, all records come in IT_GP but if not then only first line item comes. Also if I dont press ENTER after entering the first line item and and add one item (total 2) and then press ENTER then sometimes both the lines disappear.
Thanks,
Vishal