Hi Tree, that's construction history kicking in.

You can disable it by selecting the mirrored object (the newly created one), and then go to the Edit palette and run Edit > History, and then push the "Disable update" button that shows up in the options area.

With history updates for that object set to be disabled, it will no longer respond to the input object begin edited.


Also, if you move the mirrored object somewhere first (instead of moving the original first), that will also break the history as well.

- Michael