gnome-session-fallback using 100% CPU

[Larry Siden]

When I start my session, "top" indicates that gnome-session-fallback uses 100% CPU continuously.

$ lsb_release -rd
Description: Ubuntu 13.04
Release: 13.04

$ apt-cache policy gnome-session-fallback
gnome-session-fallback:
  Installed: 3.6.2-0ubuntu5
  Candidate: 3.6.2-0ubuntu5
  Version table:
 *** 3.6.2-0ubuntu5 0
        500 mirror://mirrors.ubuntu.com/mirrors.txt/ raring/universe i386 Packages
        100 /var/lib/dpkg/status

$ uname -a
Linux morpheus 3.8.0-25-generic #37-Ubuntu SMP Thu Jun 6 20:47:30 UTC 2013 i686 i686 i686 GNU/Linux

In /var/lib/AccountsService/<me>:
...
XSession=ubuntu

This also happens when I attempt to start a session with Gnome Classic.

Please tell me what other info you might need to determine what gnome-session-fallback might be doing or if there is some cache file that needs to be removed to make the problem go away.