It seems that SU tries to optimize the size of file, and it uses the same entities for Groups, until they are edited. When you copy a group, you can check that in the Entity window, it does tell you that there are several instances. BUT, you don't have the "Make Unique" feature. The workaround I found to make a group unique is simply to open it and close it.
From the Ruby standpoint, there seems to be no way to detect that a group exists in multiple instances.
In SU6, I use make_uniquemethod on Groups in a rather blind way.
In SU7, you get a warning message telling you this method is deprecated, so I thought SU7 would automatically make a group unique as soon as you apply some transformation to its entities. It does not seem to be the case.
Anyway, the bug is easy to fix. It will go to the next version. But I can't remove this bloody Warning messge from the Ruby console!
If anyone knows how to check a Group is in one or several copies in the model, thanks to advise
Fredo