It seems 2.79 Flip Names function does not work correctly.
This has caused alot of frustration for me this morning. Can you verify and pass this along so that your tutorial is accurate for the latest version?
Thanks!
I believe it is a bug. Another user brought this up to me recently. You should use the Symmetrize option instead. It's a better operator anyway, doing the duplication, mirroring, and renaming all in one click: