[Vala] Newbie question (using directive)

[Wolfgang Mauer <wolfgang mauer kabelmail de>]

Hi all,
in my source i just have

    using Gtk;

and no other using!
Now if i want to use

    public Menu menu;

i get -> error: `Menu' is an ambiguous reference between `GLib.Menu' and 
`Gtk.Menu'
But i don't have a "using GLib;" in my source !!!

Is this a Bug?

Greetings
Wolfgang