The quote below is taken from lines 387-407 (inclusive) of RFC1459,
which as far as I know is still the only valid IRC specification.

----- Quote start -----
   The presence of a prefix is indicated with a single leading ASCII
   colon character (':', 0x3b), which must be the first character of the
   message itself.  There must be no gap (whitespace) between the colon
   and the prefix.  The prefix is used by servers to indicate the true



Oikarinen & Reed                                                [Page 7]

RFC 1459              Internet Relay Chat Protocol              May 1993


   origin of the message.  If the prefix is missing from the message, it
   is assumed to have originated from the connection from which it was
   received.  Clients should not use prefix when sending a message from
   themselves; if they use a prefix, the only valid prefix is the
   registered nickname associated with the client.  If the source
   identified by the prefix cannot be found from the server's internal
   database, or if the source is registered from a different link than
   from which the message arrived, the server must ignore the message
   silently.
----- Quote end -----

The most significant part of that section is that which states:

"Clients should not use prefix when sending a message from
 themselves; if they use a prefix, the only valid prefix is the
 registered nickname associated with the client."

That is precisely the rule which Chatter breaks, since it always sends
a prefix including also the username and the userhost address.
