The SslStream does not properly send the "close_notify" alert on SSL3 and above as specified in the RFC. See http://tools.ietf.org/html/rfc5246 for the detail concerning the "close_notify" alert.
In particular, the alert is not send when the method "Dispose()" is called, and no alternative are actually offered to the send the alert.
This invalid behavior wreaks havoc when interacting with numerous 3rd parties (starting from FileZilla for example when attempting FTPS with a .NET app on the server side).
This problem has already been observed and confirmed by other parties on StackOverflow http://stackoverflow.com/questions/237807/net-sslstream-doesnt-close-tsl-connection-properly