TImage resize does not seem to affect TImage.TCanvas.ClipRect

I'm writing a backgammon game using a TImage control on a Form and when I
resize the form I want to be able to redraw the board using the new size of
the form.
I put code in the OnResize Event of the form to resize the TImage:

   Form1.Image1.Width := Form1.ClientWidth;
   Form1.Image1.Height := Form1.ClientHeight;

Unfortunately, when I try to resize the form to a size larger than it is at
startup, it seems that the Image Canvas' clipping rectangle is still the
size it was on startup.
I do an Image1.FillRect on each resize event using the Image's current Width
and Height.  Rectangles smaller than the startup width and height do get
drawn in the proper size, but larger rectangles appear to be clipped to the
startup width and height.  I tried to change the value of
Image1.Canvas.ClipRect to the same value as the Image1.Width and
Image1.Height, but it is read-only so that approach was a dead end.

Anyone understand what's going on here?