Setting boolean flag on a table

Hi,
I am using NAV 2009 NA-ENG SP1.
I have added a boolean var. IsWMItemDeletionReqd and a function SetIsWMItemDeletionReqd() to SalesLine table as below.

SetIsWMItemDeletionReqd(flag : Boolean)
BEGIN
    IsWMItemDeletionReqd := flag;  //IsWMItemDeletionReqd is a global boolean var.
END

I am calling the above function from the OnDeleteRecord() trigger of Sales Order Subform as below

Form - OnDeleteRecord() : Boolean
IF (Quantity <> 0) AND ItemExists("No.") THEN BEGIN
  COMMIT;
  IF NOT ReserveSalesLine.DeleteLineConfirm(Rec) THEN
    EXIT(FALSE);
  ReserveSalesLine.DeleteLine(Rec);
END;

// Execute WMERP code only if WM add-on is enabled
IF NOT WMI.IsWMAddOnDisabled() THEN BEGIN
  // Restrict deletion of G/L Account type of WM Sales Lines directly
  IF (Type = Type::"G/L Account") AND (WMItemNo <> '') THEN BEGIN
    MESSAGE(TEXT002);
    EXIT(FALSE);
  END ELSE BEGIN
    // Set flag to mark deletion of WM Item along with current salesline
    SetIsWMItemDeletionReqd(TRUE);
    EXIT(TRUE);
  END;
END;

And the OnDelete() trigger of Sales Line table is as below

OnDelete()
BEGIN
  ...............
  IF IsWMItemDeletionReqd THEN BEGIN
    // Delete WM Item corr. to Sales Line of type Item only. 
    IF (Rec.WMItemNo <> '') AND (Rec.Type = Rec.Type::Item) THEN
      WMI.DeleteItem(SalesHeader, Rec);  //WMI is a codeunit
  END;
END;

The objective is that when user deletes a sales line from either the Sales Quote or Sales Order form, the program first calls OnDeleteRecord() of the underlying subform wherein i first set the flag IsWMItemDeletionReqd to true in SalesLine table so that when later OnDelete() trigger of the underlying table is called, the function WMI.DeleteItem() should get called.
However the problem is inspite of setting the flag from the subform when i later access it in the salesline table, the flag is not seen as True and hence my function is not getting called.

Am i missing something?

Regards,
Hemant