Ahhh yes - behaviour works as you describe.
I was making the mistake originally of clicking on the knob itself, rather than the text label for the knob.
I can understand the reason for the implementation - perhaps it's just not intuitive without reaching for the manual. I do not recall seeing this in the printed documentation for Spark. Perhaps it's worthwhile including this in some kind of FAQ or addendum to the manual Arturia?
Thanks for your response.