Mesh Selection

Dear All,
I have loaded and visualized a STL file using RWStl::ReadFile and then MeshVS_Mesh function calls( See Attached PDF file).
The mesh comes well displayed and with smooth and fluid movements while zooming,orbiting and so on , despite about 8000 Nodes and 17 000 triangles
I am also playing around face selection of triangle mesh and it runs fine.
In fact,by calling the function
m_context->Activate(aMesh, MeshVS_SMF_Face)
the triangles of the mesh located under the mouse cursor are highlighted (as shown in fig. 2).

But on the other hand, by calling the same above function with the "MeshVS_SMF_Node" (instead of MeshVS_SMF_Face) parameter, the nodes are NOT highlighted; it does happen nothing ; I was expecting node highligths.
Any reason for this?
Where am I doing wrong?
Thanks in advance