What you'd expect when you select a site in the IIS console and choose the "stop" button is that all bound ports would stop responding, right? That's what it did in earlier versions of IIS, at least.
What I'm seeing today (on more than one server) is that, when I stop the site, the SSL port 443 stops as expected, but port 80 stays open -- and it keeps responding to requests with 404 Not Found errors!
TCPView shows that port 80 is being used by "System service" with a PID of 0. Process Explorer does not show PID 0 using port 80.
This is IIS 7.5 on Windows Server 2008 R2 x64. Is this perhaps some fancy new feature of the Windows Firewall? (The service is running, but the firewall is disabled by Group Policy.)