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This might happen when you have dual-monitor setup, press alt-tab to bring the focus on the window, the press alt-space to activate window control menu, choose "move", now there you go!
Not exactly an odd issue, happens so often. Switch to console, run `setsid unity`, this "might" fix it, if not, reboot your desktop :D
sudo apt-get install libpam-systemd # add server file to: # ~/.config/systemd/user/srv.service