I get this same behavior in 14.04. You're code effectively bombs the desktop to login, ala ctrl-alt-backspace, for me, the unity –replace. Thanks for posting though. Not easy to find any information on this. I came up with that 'always on bottom' term which is great, but before that I had nothing.
Suspicious behavior; I have libreoffice nice priority set higher then stock, I run psensors at startup, I have the alarm-clock program running at startup and in the top panel with the date. Could be something associated with applications going full screen -I don't know.
Posting this mainly for the note about the above command causing an instant log out for me. We don't like run code out of the blue or in a careless way, but sometimes when the alt-tab switcher, dash and launcher are all basically invisible, disappeared, gone, “always on bottom' mode and you're trying to avoid having to log out yet another time......
Be real, be sober.