This happened to me with 12.04, and the behavior is consistent with 14.04.
Build a fresh core using LMCE-1404-20161119175532-i386.iso. Log in via ssh and update everything. When the orbiter times out, I am shown pictures as you would expect.
Create disk less image successfully.
My first orbiter created from the image displays a clock for a screen saver. Three subsequent media directors added to the system display pictures not a clock.
Looking in the web-admin under files & media / screensaver the path is listed as /home/public/data/pictures/flickr/ and the flikr script is active. (It would have to be for the server and two other orbiters) Under advanced / configuration / devices and looking in the tree under Generic PC as MD / Onscreen Orbiter / Photo screen saver the configuration is identical among the four listed orbiters.
All of these computers are using the U1 basic interface.
Thoughts, suggestions for troubleshooting?