HeaderBar non-draggable window issue

[Michael Strauß]

> One other point: if the MenuBar is DRAGGABLE, there's no resize cursor and it's also not actually draggable, it must be DRAGGABLE_SUBTREE).

Yes, this is to be expected for most controls with non-trivial skins
(i.e. skins that have inner nodes). Since DRAGGABLE is not inherited,
inner nodes won't be draggable. It's almost always better to use
DRAGGABLE_SUBTREE to include the entire substructure of the control.