This is a guess, but what what describe sounds like a security feature. It is disallowing you to copy and paste between secure and insecure threads. Vista has this annoying feature where it required elevated permissions to cut and paste into elevated security applications.
This might be what you are seeing.
As it so happens, I have decided to run as a limited user now when using the internet so I am logging in as a limited user, after some malware installed an exe in c:\program data and would stop task manager running and take over my desktop.
I realise that security must be inconvenient but I guess that word of the moment here on Channel 9 "crippled" is what the result is.
I do also experience this issue in notepad where it is almost impossible to target............http://channel9.msdn.com/Forums/Coffeehouse/Windows-8-Copy--Paste-bug
OK, I have just tried to select channel9.msdn.com in the above URL to make it bold, and cannot as the OS has a mind of its own. I am running the admin account.
I was going to upgrade my work machine to Windows 8, that ain't gonna happen now (terrible English BTW)