Hi there,
I recently installed the demo too and think its an awesome instrument (and I’m not even particularly into electric pianos though I’m sure you could have some serious fun making lounge style break music a la Kruder & Dorfmeister et al) 
I haven’t noticed the detune issue you mentioned as yet but to be honest I have not tried to use it with other instruments particularly yet (i.e. just drums and copious quantities of effects/processing) 
Its an interesting point though regarding whether its intentional or not! 
I know little of the original machines but if they are anything like vintage synthesizers with unstable oscillators then its possible that the detune anomaly you are referring to is intended as part of the authenticity and dirt (although I’d check all the settings to be sure such as vibrato etc).
One way you could perhaps improve upon the situation as an experiment is to turn on ‘Hermode Tuning’ for the VSTi and play around with the settings, see if this improves upon it or not - just an idea? 