How to lock BW only when System is logged out?

Perhaps I am misunderstanding something. I want to have BW lock when I log out of my system or shut down my system. I select “On System Lock” but BW locks whenever I quit my browser. I think the only thing to stop this is “Never” but that would mean it never locks (of course).

Am I misunderstanding how this works? Is there no way to be able to set it so that it locks only when I log out or shut down my computer rather than whenever I close my browser? And, please don’t reply “Just don’t quit your browser”.