There are issues with mach saving CV changes during a session. Set up CV by setting G64. Also check that the other CV options are off, such as CV distance tolerance, CV feedrate, CV stop on angle, plasma, and G100 adaptive nurbsCV.
These settings are all in general config except for CV feedrate is on the settings screen. Once you have this set close and end you mach session and open mach back up. Check that your settings stuck now it should work. If you make any changes to your CV settings you MUST close mach and reopen.
Which reminds me.
REQUEST: Please put CV FEEDRATE on the general config dialog in the CV options section.