Fredo,
You are right about the group, as I was trying to say (probably not clearly), there is no problem when editing within the group.
However, if I make a simple rectangle (or other shape) in the general scene and I do not make it a group before using the plug-in; then SU crashes as soon as I enter done after using the plug-in (either for V, J or N). I have tried several times including for two faces of a cube and other forms, and every time it crashes.
Perhaps as you have no other reports of this problem, it is the fact that I am now working on an older mac which is the cause. If so please don't worry about it, I'm very happy with the excellent plug-in and can use it in a group in a separate file before putting the group in my main file. One day soon I may get a new mac!
Thanks, Paul