Fails the 2nd time around

vertex_buffer.cpp

		GLuint buffer = Gl::native_handle( *this, streamindex );
		GLenum access = Gl::ToPlatform<GLenum>( gpubufferdesc.accessflags );
		GLsizeiptr bytesize = vertices.size();
#ifdef FURROVINE_OPENGL44
		// Broken on NVidia drivers for Windows 10, 9/8/2015
		//auto map_named = gl::MapNamedBuffer;
		//auto unmap_named = gl::UnmapNamedBuffer;
		auto map_named = gl::MapNamedBufferEXT;
		auto unmap_named = gl::UnmapNamedBufferEXT;
#elif defined FURROVINE_OPENGL33
		auto map_named = gl::MapNamedBufferEXT;
		auto unmap_named = gl::UnmapNamedBufferEXT;
#endif // OpenGL 4.4 | 3.3
		void* mappedres = map_named( buffer, access );
		std::memcpy( mappedres, vertices.data(), bytesize );
		GLboolean r = unmap_named( buffer );
		if ( r == gl::FALSE_ ) {
			// panic
			throw graphics_runtime_exception( "UnmapNamedBufferEXT failed", gl::GetError() );
		}