I am now tearing my hairs out.
Surely a matter about Sioux' stratagems, and Sioux' trophies.
I am drawing on a 2D sketch.
I modify the plane containing the 2D sketch.
But, unfortunately, a basic math concept is seeming to be lost by SW during the travel : a plane has 2 faces, or to say things in other way, a 2D frame has 2 possible orientations.
Of course, when a plane is constructed, SW forgets this basic math concept (I learnt it one year before my high school diploma !!!!)
So, how can I flip a plane ?
Tx for your help, but it's really a pity that SW don't ask which orientation (among the 2 possible), has to be chosen for a construction.
If SW was written by Dassault enginers, it's not amazing that Dassault planes are falling from time to time.