Hi Burr, yup that is the way to track it down.

The way the button works is it does some different functions if you do Ctrl+click on it (unlock subset) or if you right-click on it (isolate lock - locks everything else than the selection).

You can't really "right-click" on a keyboard shortcut, so probably if you wanted to set those up for keyboard shortcuts they would be separate shortcuts, like one for "L", one for "Ctrl+L", one for "Shift+L", etc...

- Michael