Images from GUI Bloopers, by Jeff Johnson. Used without permission.
What's wrong with this?
What can you do about this?
Make sure that other panels only display secondary selections, and bump down previous primary selections to secondary selections, once the user has made another primary selection.
Be a "good citizen" in the operating environment. Register your application's presence with the selection manager. When your application loses focus, dehighlight any primary selection, but keep track of it. Notify the selection manager when your application comes into focus.
Exception: when you have multiple views of the same data, the primary selection may exist across the same data selected in each window.