Comment 9 for bug 1107850

This seems to be some interaction with GDK applying shapes to child windows.

Before GTK maps the toplevel window, it issues a ConfigureRequest to resize the window. Probably because this request may be redirected to and modified by the window manager, though I'm not sure it would be for an unmapped window, GDK does not record the new size on the window until it receives the ConfigureNotify reply.

Immediately after the toplevel is mapped, GDK sets a shape on the child window. This is based on parent window sizes - probably some client-side window code that doesn't really make much sense for the server-side toplevel window size. GDK still considers the toplevel to have the size it had before the ConfigureRequest, which happens to be the default GtkWindow size of 200x200.

The child window has a back pixmap of None, meaning it shows nothing until it is drawn, and so the background remains. The toplevel window has a back pixmap or background color based on the theme and so looks inconsistent.

Some options I'm thinking about:

1) Change the default size of the window. This needs to be done before realizing the window, but the desired size is not provided at that point. A small size could be selected to limit the effect to 1 pixel.

2) Try sizing the window as soon as possible instead of waiting until Show.
The event loop would need to run to process the ConfigureNotify, so this may not be helpful.

3) Look into setting the back pixmap of the toplevel window to None.

4) Don't set the back pixmap of child windows to None.

5) Find out why dlbi changes made this show up.