When the maintainer of the Urban Terror 3.0 ebuild upgraded the ebuild to Urban Terror 3.1 I don't think he/she realized that UrbanTerror31.zip is only available in the form of an upgrade and you need to extract UrbanTerror31.zip coupled with urbanterror3.zip to have a working install. At the moment I think that's why it's not working for me.
3.1-r1 fixes this
way to lie to me mjc
This issue has not come up agian so I'm marking this bug closed