I have the same problem and configuration.
When intended to uninstall i read this in package information.

NOTE: The artwork for PlaneShift is not included in this package. You can get the data from a Planeshift release or use the Planeshift updater.
NOTE: To play the game you must be in the group 'games'!

I used the installer and it worked!
Quite easy to use. You can follow the ubuntu tutorial. And it has an uninstaller that's rare, but cool.

muli