nm-connection-editor: broadband editing impossible ("No agents were available for this request")

I can create a new mobile broadband connection in nm-connection-editor using the wizard, but when I try to look at it from the list of available connections (selecting the connection, clicking "edit"), I get dialog box "Error initializing editor" / "No agents were available for this request". There are no messages in the terminal from which I run nm-connection-editor (besides bunch of css warnings).

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: network-manager-gnome 0.9.2.0+git.20120126t000800.5151959-0ubuntu4
ProcVersionSignature: Ubuntu 3.2.0-18.29-generic 3.2.9
Uname: Linux 3.2.0-18-generic x86_64
ApportVersion: 1.94.1-0ubuntu2
Architecture: amd64
Date: Mon Mar 12 23:49:41 2012
IfupdownConfig:
 auto lo
 iface lo inet loopback
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release amd64 (20101007)
IpRoute:
 default via 10.0.0.138 dev wlan0 proto static
 10.0.0.0/24 dev wlan0 proto kernel scope link src 10.0.0.2 metric 2
 169.254.0.0/16 dev wlan0 scope link metric 1000
NetworkManager.state:
 [main]
 NetworkingEnabled=true
 WirelessEnabled=true
 WWANEnabled=true
SourcePackage: network-manager-applet
UpgradeStatus: Upgraded to precise on 2012-03-11 (1 days ago)
nmcli-dev:
 DEVICE TYPE STATE DBUS-PATH
 wlan0 802-11-wireless connected /org/freedesktop/NetworkManager/Devices/1
 eth0 802-3-ethernet unavailable /org/freedesktop/NetworkManager/Devices/0
nmcli-nm:
 RUNNING VERSION STATE NET-ENABLED WIFI-HARDWARE WIFI WWAN-HARDWARE WWAN
 running 0.9.3.0 connected enabled enabled enabled enabled enabled