When I have the sample code below in a basic C++ project and type Geometry:: I get a suggestion for _vertex and not Vertex.  If I change the osg namespace to abc I correctly get Vertex.  Does VA X do something special with the the osg namespace.  I did not include osg in my test just the sample code.
namespace osg {
    class Geometry {
    public:
        double _vertex;
    };
};
namespace Geometry {
    class Vertex {
    public:
        double x,y;
    };
};
I have VS2005 and VA X 10.4.1640.0