Multi-monitor: spaces thumbnails on external monitor missing I've been having the following issue since about two weeks:

My external monitor, containing the OS X title bar, does not show the thumbnails for my three spaces when in mission control. My retina's monitor (secondary) does show them as before.

[ Nice, this question need a screenshot, but I don't have enough reputation. :( ]

External (primary) monitor:

No grey border in mission control. The outermost bg is the wallpaper for that space on the Retina display. It will change as well when moving to another space using ^left/^right

I can still move an app to another space by drag 'n dropping them to the place where the thumbnail should be. So it's not that they're gone; they're just invisible!

Retina display (secondary)

As it should be in mission control: Zoomed out bg image, grey border containing three thumbnails for the three spaces I have.

Has anyone experienced these symptoms as well?
Restarting your Dock should do the trick. To do so just open the Activity Monitor, type dockand press End Process.