Revers Face issue

[Davidfi1]

Hi
Sometimes Sketchup reverse faces of objects.
This is usually no issue but in SketchyPhysics ... look what happens:
Reverse Face

It is very wired that after playing with a working model
it just stops working.

The reason is that sketchup reversed some faces making SketchyPhysics stop working or doing completely different things.

The above model is the simple "floor" with the top selected and right click "Reverse Faces"

FYI.
David.