dynamic highlight of mesh - first and second order

Ciao
in the two attached pictures you can see what is happening when I hover the mouse
on the mesh of a cube, when the mesh is a first order one, and when the mesh is second
order. In particular here the mesh is all tets (4 and 10 nodes for 1st and 2nd order)

If the mesh is first order the right triangle is highlighted; if the mesh is second order
a triangle not "under" the mouse position (indicated for the two cases by the arrow)
is highlighted.

Obviously the same thing happens for selection, and also for the
dynamic highlight/selection of 3D elements.

Any idea
Grazie mille
Giovanni