Sometimes xscreensaver will prompt the user to enter their password thinking they are trying to unlock the computer.
This is annoying!
xfce4-power-manager is simulating fake KeyPress events.
This basically means your computer thinks someone is pressing the keyboard and thus stops your screensaver and offers a login menu.
This will usually happen every 30 seconds or so.
The instant solution is to close
More permanent Solution
I never had any issues removing the power manager on any pc I have worked on.
sudo apt-get remove xfce4-power-manager