@Keet
You've right! I've test it and I can seen the bad results.
More than what you already observe I've seen more objects than I want when multiply groups.
In the last Group-M it need to have ONLY others 5 Group-M but I have also another set of ungrouped items for every group.
That's not good.
I've also receive a lot of errors in the console.
I will se what I can do.
Until than a workaround:
After undo and some ghost objects remain in 3D, try to minimize the 3D and restore it back (use the small arrows).
The ghosts will disappear. It's a temporally solution.