After plugging and unplugging external monitor "App" launcher menu is offscreen

[AlanGriffiths]

I added and removed an external monitor several times during testing. And while plugged in I used the launcher on the external monitor.

After unplugging, Ctrl-Alt-A took focus from the current app, but the App menu wasn't displayed. However, it could be used (so was apparently still offscreen).

[AlanGriffiths]

I've tried to reproduce this and not yet hit on the right sequence of actions. So far it works correctly every time.