This was resolved for me after shutting down and restarting. The Unity application launcher now correctly appears in front of any other window.
For me the
unity&disown solution didn't work - it actually made the entire unity UI permanently disappear until restarted, including the top part of every window with the close, minimize and maximize buttons. Even after waiting ~20 minutes the UI didn't reappear and I couldn't close any windows to see if there was possibly a dialog box waiting for my response hidden somewhere, so I had to force a shutdown by holding the power button for 4+ seconds.
The issue occurred after suspending and waking up my machine several times, although I'm not positive the two events are correlated.
Hope this helps anyone else having trouble with the