Comment 1 for bug 1473096

I confirm this. I've installed Caffeine through AppCenter. When I launch it, its icon appears on Plank for a couple of seconds and then... gone. Running via terminal outputs this:

>caffeine
/usr/bin/caffeine:25: PyGIWarning: Gtk was imported without specifying a version first. Use gi.require_version('Gtk', '3.0') before import to ensure that the right version gets loaded.
  from gi.repository import GObject, Gtk, GLib

and it stays there...