copying from shapes to masks

SPECIFICALLY: Fourth Line of this page, 3rd point, above:

"Convert a shape path to a mask path by copying the shape’s path to the Mask Path property."

THIS most useful of things DOES NOT WORK!!

How do you get around this?

How did this make it into the current documentation? 

Is there some obscure trick to this?

I'm creating a shape layer. Then creating a Hexagon Shape within that layer with the Polygon Tool.  I then create a Mask in that same layer.  I then copy the Shape Path and attempt to past it into the Mask Path, as per the above line.  You can see what I'm doing in this screen shot:

http://imgur.com/WZ7Wd

It does NOT create a mask, 

Instead a new group is created, Group 1, with a duplicate of this shape in it.  So no further forward.

Anyone know the way to do this?