Membership - configuring level with both positive and negative shortcodes

I'm working through my first setup - added a new level, dragged shortcodes from the sidebar into Negative rules, checked the two shortcuts.

But how do I drag Shortcuts to Positive rules so I can set the one shortcode I want as a positive rule?

Once I drag Shortcodes to either neg or pos rule, that's it, it's not available.

Here's a screencast:

(Mac, Chrome browser, fluency admin, current release (not beta) of Membership.)