Pose Libraries...what am I doing wrong???

I have a rigged and skinned figure.  I have a Rest Position with all rotations, scale, etc removed.  

• I go to Pose Position and then go into Pose Mode.
• I move an arm, then hit the '+' in the List of Poses, and choose Add New (doesn't really matter which one I choose, the same thing happens, AFAICT).  Cool.
• Exit Pose Mode.

Now my understanding is each Pose is separate and not cumulative (perhaps that's wrong).  So let's create another pose.

• Still in Pose Position, get back into Pose Mode.
• Clear all rotations, scale, etc.
• Move the leg and Add New.
• Exit Pose Mode.

Now clicking on the magnifying glass for Pose #1 returns the pose to default 0 position (no rotation, scale, etc.)  Clicking on the Pose #2 moves the leg.    Why doesn't clicking on Pose #1 move the arm and return the leg to 0 position?

Can someone explain how I'm supposed to be using the pose library?  This is 2.79b on a Mac, if that's at all relevant.

Danke!