Remove Environment map issue

I have a scene with some objects and materials.
In the scene I have also a bitmap as Environment Map.

Opening the Map Browser, at the Scene Material tab I can see the list of all materials in scene, environment map included.

In the script editor I run this line:
environmentMap = undefined

Then, in the Scene Material list I see the environment map disappear... and in the Environment dialog, the Environment turned to "None"

Now I run this line:
for mat in scenematerials do print mat

The Script Editor returns all the material list, environment map INCLUDED!!!!

Why?? Why the "Scene Material" tab and the "scenematerials" system global doesn't match?

Where I'm wrong?