I have Windows 7 RC build 7100 (+ updates) 64 bit. Some weeks ago when I was installing, I tried to remove (disconnect, de-join whatever) Homegroup (don't have another PC with windows 7 anyway...). The result was that I lost all access to the local hard disks, including volumes that never had Windows 7 on. There was nothing I could do to restore it, I could not elevate anything because the local hard disk was not available (access denied). Finally I had to re-install one partition on my HDD (make the Windows 7 partition inactive) , activate the administrator, and gain back control. Took me hours and hours. I suggest you activate the local administrator before you try to re-produce the bug...

Anyone tried it?

I technically "tried this" but by accident. Thankfully it only effected my data drive so just activated administrator and added the permissions for users i doubt i would have thought of that if not for the above post however, thanks :) system is 64bit RC Build 7100 same as OP