Sometimes mirroring of multiple identical Synchronous features fails,
especially when the features had been previously "attached" - usually after
placing them by using Feature Library.
Solution "Mirror" command contains an option to "Detach Faces". Using this, you will get
a set of faces (instead of failed features) when mirroring. After this, you can
manually attach each of the mirrored faces to the part.
Notes and References IR#7880142
Hardware/Software Configuration Platform: INTEL
OS Version: 864