I just wasted some time cleaning up a little mess I seem to keep making periodically. It is pretty basic stuff, but subtle and easy to overlook. I don't remember it getting a lot of emphasis in all my training - maybe I missed it.
Scenario 1: Create object X. Duplicate (shift-D) to object Y. Add animation to X. Add animation to Y. Animations (actions) are independent.
Scenario 2: Create object X. Add animation to X. Duplicate (shift-D) to object Y. They both have references to the same animation (action).
Of course everything is working exactly as designed... Practically, the material reference that is copied behaves like a value and is easily changed in the properties panel. The action is also a copied reference, but has different implications. Obviously you can break the link several ways (going a little deeper):
Maybe this rant at myself will help me to remember/improve workflow. Hopefully no one else falls into this trap - does anyone sympathize?