Comment 8 for bug 483474

Since I posted this morning I have set all my screensaver and power settings to 'never', which did stop the problem then I went to ~/gconf.d and deleted the contents and rebooted.
The problem has not occurred now for 5 hours so perhaps is fixed (let's see) but I have no idea what the cause was. I am going to put my settings back to 15 minutes and see if anything changes.