Something does not add up

Can anyone explain to me:

1. why gr_ship.ship_charge does not display as 0.00 in the first DISPLAY line?

2. why gr_charges.order_total appears to disappear?

CODE
  IF gr_charges.ship_charge = NULL
  THEN
    LET gr_charges.ship_charge = 0.00
  END IF

  LET gr_ship.ship_charge = gr_charges.ship_charge

   DISPLAY "AOT: ", gr_charges.order_total, " SC: ", gr_ship.ship_charge
   SLEEP 5
  LET gr_charges.order_total  = gr_charges.order_total + gr_charges.ship_charge

   DISPLAY "BOT: ", gr_charges.order_total, " SC: ", gr_ship.ship_charge
   SLEEP 5

RESULTS:
AOT:           268.1250 SC:
BOT:                    SC:

These elements are defined thus:

  DEFINE  gr_charges
    RECORD
      tax_rate      DECIMAL(5,3),
      ship_charge   LIKE orders.ship_charge,
      sales_tax     DECIMAL(16,4),
      order_total   DECIMAL(16,4)
    END RECORD

  DEFINE  gr_ship
    RECORD
      ship_date     LIKE orders.ship_date,
      ship_instruct LIKE orders.ship_instruct,
      ship_weight   LIKE orders.ship_weight,
      ship_charge   LIKE orders.ship_charge
    END RECORD


And orders.ship_charge is defined like this in PostgreSQL:


ALTER TABLE public.orders
    ADD COLUMN ship_charge numeric(16,4);

COMMENT ON COLUMN public.orders.ship_charge
    IS 'Shipping charge';

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James B. Byrne                mailto:[email protected]
Harte & Lyne Limited          http://www.harte-lyne.ca
9 Brockley Drive              vox: +1 905 561 1241
Hamilton, Ontario             fax: +1 905 561 0757
Canada  L8E 3C3