xpra package points to unmaintained/abandoned version
Some users have complained that they could not install the latest versions, ie: http://lists.devloop.org.uk/pipermail/shifter-users/2013-October/000740.html
The version currently linked to has not been updated for over 3 years. It does not build properly, it does not run against any of the versions shipped by all the major distros. All said distros have switched to the "new upstream": http://xpra.org/
Let me know if there is anything I need to do to help you update the link.