When the file transfer is disabled,  the following items are still visible in the menu of the NoMachine Monitor (the !M application running in the system tray):

Show transfer status

Send a file from the client

Download a file from the server

Only when clicking on any of such menu entries the user is informed that file transfer is disabled, while it would be more appropriate to completely remove these items from the menu. 

This problem occurs only in case of virtual desktop sessions.