OK.
Thanks, Pilou and Michael.
Thanks a lot for your explanation, Michael.
You are right for the problem. The little shelf is an error, and not desired. I don't know how i arrived at this. An error from me, sure. Now I understand.
The result, with render with cinema4d :
http://jipsou.free.fr/frc4d/Objets/PiedACoulisse01-53P.jpg


So thanks a lot, and congratulations for your soft.
I continue my exploration.