I use Internet Sharing at work to create a local WiFi network (sharing the GigE connection) for my various iOS and tablet devices to connect through. After the 10.7.3 update, I cannot turn sharing off after I unplug the Ethernet cable. All the checkboxes in the system pref pane are cleared, but I am unable to join a WiFi network.

After I plug the Ethernet back in, I can then disable sharing, but only while it's plugged in.

As best I can guess, there might be some xinetd cruft laying around, but I haven't the slightest clue as to how to look for it or fix it. Any ideas?