Navigation Popups is a gadget that works a little like the Page Previews beta feature, except that it gives previews of all types of links, not just page titles. It's very useful with Recent Changes, because, among other things, it lets you preview diffs of changes without having to visit the page in question. It does this by opening a little popup overlay that shows the diff. Navigation Popups is a popular gadget, with almost 67,000 users.
In Live Update mode, the gadget tends to get "stuck," meaning that individual overlays will decide to hang around on the screen. Normally, a popup disappears as soon as you move the cursor off either it or the link that spawned it. But in Live Updates mode, when a popup gets stuck, there's no obvious way to get rid of it. You can scroll away or click elsewhere on the page. The only thing that clears it is a page reload. The overlay is untethered to its link, and even stays on top when you open a menu (as shown in the screenshot below).
This may well be a bug in the gadget itself, technically, rather than in Live Updates. But I'd like to get this fixed, given the gadget's popularity and usefulness to Recent Changes patrolling, and how bothersome it is when it blocks menus and content.
Screenshots of "Stuck" popup in Live Update mode