![Da bounct der Moni :dex:](./images/smilies/dex_bounce.gif)
If SevenDex, Dexcube, task switcher or full-screen preview display black preview thumbnails, the debug option 'Disable full-screen preview' might have been activated.
Open 'Settings > Plugins and Extras > Advanced' and uncheck 'Disable Full-screen preview'. Switch your desktops and try again.