[Lazarus] Should Frames be transparent?

[Tony Whyman]

I suppose that this could be one of those "is it a feature or is it a 
bug" type questions, but it is also a big difference in behaviour 
between Linux and Windows.

I've realised that if you create a simple application with an image on a 
form and then partially or wholly overlay it with a frame or a even a 
radio group then:

- On Linux: the frame and radio group are not transparent and obscure 
the image.

- On Windows: the frame and radio group are  transparent, have no 
background, and the image shows through.

This applies to both IDE and a running program.

In the windows version, I came readily make the frame opaque when the 
program runs by simply overriding its Paint method as follows:

procedure TFrame1.Paint;
begin
   EraseBackground(Canvas.handle);
   inherited Paint;
end;

So the reason for the transparency is also certainly that the frame's 
background is not being erased under Windows but is being erased under 
Linux.

So bug or feature?