Web sharing is displaying MAC address

I've just noticed that in the Web Sharing section of the Sharing preferences panel, my computer is being referred to by its MAC address and not the address specified in the dialog box.

A screenshot explains it better:



If I edit the name and click OK in the dialog box, the correct name will flash up for a split second, but then the MAC address will return.

also, the correct name is shown at the top of the panel.

Any ideas?