Huh. I realise now that I've never used that before, and that on an existing install of NativeCAM it does the same thing. It changes whatever value is in the field, to a default, and then back to 25.4 x that default.
So whatever is in e.g. the Diameter field, it'll change to 45, then to 1143, then back to 45 etc. as if doing an imperial to metric conversion and vice versa.
I'm not sure what the original authors intended here as; I don't know why you would want to enter gcode instead of a numeric value in what I understand to be a numeric-value-only field. If it said 'change to imperial' rather than 'to gcode' it would make sense, but it'd be broken, as it doesn't preserve whatever value you enter when it does the conversion.
So I suppose if you feel like it, you could change the wording to imperial/metric as appropriate and see if you can make it work! That seems like a rather low priority thing though.