This no longer happens if I use gdm3 as my x-display-manager. That solves the mystery of when it stopped working: the first time I tried to change my network settings after dropping Gnome3.
So this might be a bug in both slim and xdm (both of which I've tried), or it might be that network-manager is expecting something non-standard. -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected]

