Created attachment 25006 [details]
Image showing problem

This is what happens:

     - When the expander is expanded, the "extra" area
       gets gtk_widget_show() called on it.

     - This causes the extra area to be queued for a draw

     - In the idle loop the area is not drawn because it overlaps
       the dialog's button area, and so gets clipped out by
       gtk_container_propagate_expose()
 
     - The configure event arrives, and the dialog is size allocated.
       Because of bugs in the GtkWindow size allocation 
       logic where GtkWidget->allocation is sometimes out of sync with
       the actual window size when gtk_widget_queue_draw() is called,
       this doesn't cause the window to be invalidated.
           (Normally not a problem, because windows are just gray
       like their background color anyway).

     - The FileChooserDefault gets size allocated, but this doesn't
       cause a redraw because FileChooserDefault inherits GtkVbox
       which calls gtk_widget_set_redraw_on_allocate (widget, FALSE);
       on itself.

     - So, only the areas that get redrawn for other reasons (ie. 
       the buttons) actually get drawn.

A simple fix is to simply call

     gtk_widget_set_redraw_on_allocate (impl, TRUE) 

in gtk_file_chooser_default_init().

Committed this as a work around.

*** Bug 145352 has been marked as a duplicate of this bug. ***