OK i have find that I miss! :)
It was "select all edges"!
For me i have understood "all edges" who are "all edges" not merged on my "bottom" face! (so "one edge" of the surface)
:)

Now with selecting all "4 edges" of the surface all works fine! :)

...but maybe my method by kill the surface and redraw by a Sweep with the "3 good edges neighbour" is more speedy...