Code behaves differently in Android and Windows

Code behaves differently in Android and Windows

I try to draw on a bitmap. This works fine in Windows but creates a
segmentation fault in Android (anyhow, that's what Delphi says, I just see
no reaction on Android). I have a mobile project, form containing only a
TToolbar, TSpeedButton, two TLabels and a TImage. There's just one
eventhandler for the TSpeedButton click.
When I comment out everything below the comment the code works fine in
Android. When I try to follow with the debugger the code works fine to the
end of the procedure. without seeing a drawing or a segmantation fault.
When I let it run on the fault occurs.
What am I doing wrong?
procedure TForm2.Button_DrawClick (Sender: TObject);
var rct: TRectF;
h, w: Int32;
begin
h := Trunc (Image.Height);
w := Trunc (Image.Width);
Label_Height.Text := IntToStr (h);
Label_Width .Text := IntToStr (w);
rct := TRectF.Create(20, 20, w - 20, h - 20);
// can be commented out below //
Image.Bitmap.Create (w, h);
if Image.Bitmap.Canvas.BeginScene then
try
Image.Bitmap.Canvas.Stroke.Color := $FF0000FF;
Image.Bitmap.Canvas.StrokeThickness := 3;
Image.Bitmap.Canvas.DrawEllipse (rct, 20);
Image.Bitmap.Canvas.Stroke.Color := $FF00FF00;
Image.Bitmap.Canvas.DrawRect(rct, 0, 0, AllCorners, 40);
finally
Image.Bitmap.Canvas.EndScene;
end; // try..finally
end; // Button_DrawClick //