Re my comment above -- https://bugs.launchpad.net/ubuntu/+source/gnome-session/+bug/93291/comments/13 --
Installing the recommended driver for my Nvidia graphics card seems to have fixed this.
Re my comment above -- https:/ /bugs.launchpad .net/ubuntu/ +source/ gnome-session/ +bug/93291/ comments/ 13 --
Installing the recommended driver for my Nvidia graphics card seems to have fixed this.