I have discovered that this happens if a window has the atribute keep_above setted to true.
This can be useful:
http://valadoc.org/#!api=gtk+-3.0/Gtk.Window.set_keep_above
I have discovered that this happens if a window has the atribute keep_above setted to true.
This can be useful:
http:// valadoc. org/#!api= gtk+-3. 0/Gtk.Window. set_keep_ above