Comment 49 for bug 562742

A possibly relevant piece of information on this issue:-

I installed Windows Vista to a spare drive in order to test some stuff. Among the zillions of Windows updates was one for the ethernet driver. I discovered that the updated Windows driver was causing similar problems - changing the MAC address so that I had to turn the computer off completely before restarting, if I wanted the original address back. Reverting to the earlier driver solved the problem.

If any of you folk having problems are running Windows, it could be something to be aware of.