Delphi SelectClipRGN hides bitmap

I am drawing my own background (derived from TGraphicControl) with border. After drawing the border in the DrawBorderRect function, I return the client area and want to constrain my future painting to this new region. Everything works if I don't use ClipRgn.

Working code:

var
  R : TRect;

begin;
  R := GetClientRect;     //(R -> 0, 0, 300, 200)
  R := DrawBorderRect(R); //(R -> 20, 20, 280, 180)
  Canvas.StretchDraw(R, FBitmap); //FBitmap is a 3 pixel x 3 pixel square
end;

      

        
        
        
      

    

The above code gives me the following:

But I want to use ClipRgn and I tried the following. This time the template is not displayed (but if I click on the area, the pattern appears. So it works like a working, but then gets overwritten for some reason?).

Problem code:

var
  R : TRect;
  ClientRegion: HRGN;

begin;
  R := GetClientRect;     //(R -> 0, 0, 300, 200)
  R := DrawBorderRect(R); //(R -> 20, 20, 280, 180)

  ClientRegion := CreateRectRgn(R.Left, R.top, R.Right, R.Bottom);
  SelectClipRgn(Canvas.Handle, ClientRegion);
  try
    Canvas.StretchDraw(R, FBitmap); //FBitmap is a 3 pixel x 3 pixel square
  finally
    SelectClipRgn(Canvas.Handle, HRGN(nil));
    DeleteObject(ClientRegion);
  end;
end;

      

        
        
        
      

    

and I get this (unless I left click, in which case I see above)

Any ideas as to what is going on and what I am missing?