Stringgrid - don't understand failure to update a cell

[jbmckim]

In the code below strTest updates correctly on the call to ...WvLengthSetting();.  However, the subsequent update of strTest, (i.e. strTest := InputStringGrid.Cells[WAVELENGTH_COL,iWvLngthBeingSet]) returns the value the cell contained prior to the attempted update.  (Insert swearing emoji here.)

This is called from a timer but the grid is in the same Unit as the timer.

Code: Pascal  [Select][+][-]

1. procedure TExitMainForm.WaveLengthBySpecTimerTimer(Sender: TObject);
2. const
3.   WAVELENGTH_COL : integer = 8;
4. var
5.   strTest : string = '';
6.  
7. begin
8.  
9.   if (SpecWvLengthSetupForm.Visible = false) then
10.    begin
11.  
12.      strTest :=  SpecList[iWvLngthBeingSet].WvLengthSetting();
13.  
14.  
15.      InputStringGrid.Cells[WAVELENGTH_COL,iWvLngthBeingSet]
16.                        := SpecList[iWvLngthBeingSet].WvLengthSetting();
17.  
18.      strTest := InputStringGrid.Cells[WAVELENGTH_COL,iWvLngthBeingSet];
19.  
20.      iWvLngthBeingSet := -1;
21.      WaveLengthBySpecTimer.Enabled := false;
22.    end;
23.  
24. end;            

[Blaazen]

Code looks fine.  Put breakpoints or writeln(); commands between lines to see what actually is in cell and in strTest.