Hi Alan,
The solution to the described behavior is relatively simple:
The Left Voice is memorized in Registrations with the "Style" tick, NOT with the "Voice" tick. So if "Style" is not ticked when you memorize the panel settings to a registration button, the Left Voice will NOT be memorized.
To memorize the Right Voices, "Voice" and "Harmony" ("Keyboard Harmony") must be ticked, for the Left Voice, as I said, "Style" as well.
If you want to create a pure "Voice Reg" that will later switch the Left Voice, but NOT the current STYLE, you have to use a little trick:
Copy any style to a USB stick that you only use for this purpose and rename the style to e.g. "Dummy". Now load this style from the USB stick. Make the desired settings for the Keyboard Voices. Memorize the settings to the desired Registration buttons with the "Style" box ticked and finally save the Registration Bank. Now remove the USB stick on which the Dummy style is stored. The registrations in question can no longer find this style and therefore only the Left voice is changed (and the Right voices if the "Voice" and "Harmony" boxes were also ticked), but not the style.
Hope this helps!
Best regards,
Chris