Q: Any justification for failing RSET?

Hi,
a matter of curiosity....

I have a tool running that tries to verify email addresses (reasons 
irrelevant here) - the sequence of commands used is EHLO, MAIL FROM, RCPT 
TO, RSET, QUIT (VRFY being more-or-less useless these days).
I noticed that a few large sites are returning 554 on the RSET, with the 
text "Transaction failed" - hotmail.com in particular.
Now, this is obviously in violation of RFC 2821, but I wonder..... does 
anyone have any idea of why they're doing that?
                      Harald, curious....