Comment 3 for bug 886892

thank you for your bug report, that's because you get unity-2d (the non-3d fallback option):

 Error: command ['/usr/lib/nux/unity_support_test', '-p', '-f'] failed with exit code 1: X Error of failed request: BadRequest (invalid request code or no such operation)
   Major opcode of failed request: 155 (GLX)
   Minor opcode of failed request: 19 (X_GLXQueryServerString)
   Serial number of failed request: 21
   Current serial number in output stream: 21

that seems a fglrx driver issuer