In _Rotate, if you select Copy=Yes then Rhino will accept neither an angle nor a second reference point so you can’t complete the action. If Copy=No the same object can be rotated fine.
Works for me in Version 6 SR8 (6.8.18219.371, 8/7/2018)
Well actually, on review it works for me too - the result of the rotation coincided with another object, there was no feedback that a copy had taken place and the prompt remained in place as though nothing had happened so I thought it wasn’t working.
Maybe the documentation could be improved to tell us that the command allows multiple copies until you escape the loop and/or maybe the command history could say “rotated copy made” or some such.
Now I just need to go and delete the surprisingly large number of duplicate copies I made…