Problem deriving GLArea widget

[Bill McGrory <wdmcgrory gmail com>]

I am trying to derive a widget off of Gtk::GLArea,
when I do, I get GLib-GObject-CRITICAL **: g_value_take_object: 
assertion 'G_IS_OBJECT (v_object)' failed
and "OpenGL context creation failed.

I have tracked this to
GdkGLContext* GLArea_Class::create_context_callback(GtkGLArea* self)

where a different path is taken whether or not the GtkGLArea self is 
derived or not.
However, I don't know if I am not doing something correctly, or if this 
is a bug.

Any help would be apprectiate.

the following example demonstrates the problem under a ubuntu 16.04.

TIA
Bill

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