From Dmitry Yemanov:
It has been discovered recently (thanks to Eugene Kilin) that Win32 builds of Classic Server did not set up some socket options properly, including SO_KEEPALIVE. So if you have troubles with “zombie” processes not terminating after the keepalive internal, this is the reason. The patch has been committed into HEAD today and it will be available in the v2.0 RC2 release.
Also, Windows builds (both SuperServer and Classic) are now in sync with the POSIX ones and also have the Nagle algorithm disabled by default. If you want to change this behaviour, set the config option TcpNoNagle to zero.