Comment 5 for bug 1074657

I also have this problem. Steps to reproduce:
1) Open software sources (as regular user)
2) Goto "Other Software" tab
3) Remove entry

Result:
Authorization failed.
Software sources can't be changed without permission.

When running Software Sources with massive debug I get no debug error:
software-properties-gtk -m

dbus properly registers software-properties-gtk

This is very frustrating because nothing seems to be giving out error messages. The following logs show no errors:
/var/log/syslog
/var/log/ConsoleKit/history
/var/log/messages
/var/log/dmesg
/var/log/kern.log