[syslog-ng] Syslong Agend for windows not sending MARK messages

The syslog-ng Agent for Windows 4.0 manual states "Similarly to the Linux version, the agent now sends MARK messages to the server to indicate that the client host is alive but there are no log messages to send. A MARK message is sent every ten minutes." but running version 4.0.1 does not send these MARK messages. We see lots of other messages from the host in our syslog server, but not the MARK messages. Any suggestions? Evan.