This is really nasty.
IE & IIS are handling TCP/IP connections in a non-standard way to speed up connections when both are used together. Normally a web browser does a handshaking & synchronization sequence before sending the request, but IE will send the request immediately, which IIS will respond to, while other servers will reject it, and it will then fall back to a standard handshaking sequence.
I’m not sure if the Mac version of IE does this as well, but I doubt if it does, since it doesn’t display any enhanced performance with IIS servers.
It's not only nasty, it's also entirely fictional.
There is no protocol violation whatsoever, only the old bug of browsers sending into half-closed connections (which decreases, not increases, performance).
Typical slashdot discussion, no verifiable content.