Run attached application.

Notion: none - NONE_MODAL, app - APPLICATION_MODAL, win - WINDOW_MODAL.

to reproduce:
Instance 1.
click "init"
in stage0 click "win" (note this place)
close stage0
close stage1

I see output:
(<unknown>:30038): GLib-GObject-CRITICAL **: g_object_get_data: assertion `G_IS_OBJECT (object)' failed

(<unknown>:30038): Gtk-CRITICAL **: gtk_widget_set_sensitive: assertion `GTK_IS_WIDGET (widget)' failed

(<unknown>:30038): Gdk-CRITICAL **: gdk_window_restack: assertion `GDK_IS_WINDOW (window)' failed

(<unknown>:30038): Gdk-CRITICAL **: gdk_window_focus: assertion `GDK_IS_WINDOW (window)' failed

Instance 2.
click "init"
in stage0 click "none" (note this place)
close stage0
close stage1

I see output:
(<unknown>:30038): Gdk-CRITICAL **: gdk_window_restack: assertion `GDK_IS_WINDOW (window)' failed

(<unknown>:30038): Gdk-CRITICAL **: gdk_window_focus: assertion `GDK_IS_WINDOW (window)' failed

Instance 3.
If you click "app" in noted place, no assertions fail.