Uniqueness of &rest arguments

[OLDMAN@USC-ISI.ARPA]

Are &rest arguments guaranteed to be copied?  Consider the following:

    (defmacro m (&rest args)
         `',(nreverse args)        ; Destructive reverse
    )
    (setq x '(m a b c d))
    (eval x)

What is the final value of x?   I think that I would argue that
it is undefined since args may or may not be a copy of the original
form.   Is there anything in Cttl that clarifies this?

-- Dan