Btw, there's a real bug in /socklisten, it fails to report a bind() error if you listen to the same port

The latest versions of mIRC use the SO_REUSEADDR setting to mitigate issues relating to TCP_WAIT, which many users have reported over the years. This setting means that bind will not return an error when you attempt to listen on a port that is already in use, if that socket has SO_REUSEADDR already set.