- Open your browser's developer console to the Net tab.
- visit a Flow board like http://en.wikipedia.beta.wmflabs.org/wiki/Talk:Flow
- Hover over the sort indicator ("Newest topics v" or "Recently active topics v")
- You don't see the tooltip for the sort.
- Popups makes its API request for extracts|pageimages|revisions|info for the title "You are currently reading the newest topics first. ...", but there's (probably) no page with that title so it returns "missing".