When using the Refine Radius Tool in the Refine Mask dialog cmd+option+z used to allow me to go back and revert multiple brush strokes if I wanted (and cmd+shift+z enabled redo, like everywhere else in PS).
This simply does not work anymore using Photoshop 2015.1.2 and OS X 10.9.5.
I don't know what has happened to my brain, I could have sworn that I've done that many times. I just went back to an older version of PS that I still have installed (14.2.1) and of course you are right, it does not work there either. I am sorry for having taken up your time.