Do the following:
1. As root edit /Applications/NoMachine.app/Contents/Frameworks/etc/server.cfg
2. Change #SessionLogLevel 6 to SessionLogLevel 7
3. Restart nxserver command: /Applications/NoMachine.app/Contents/Frameworks/bin/nxserver –restart
4. Try to reproduce problem.
5. Send /Library/Application\ Support/NoMachine/var/log/nxserver.log. Either attach it here or submit to forum[at]nomachine[dot]com.