Hello drfireball,
yes this feature was planned for the release, but did not have been implemented on time.
Of course, some people , just like you, told us it would be more comfortable to have the voice or sample button locked for a better preset browsing experience.
the good news is that i can confirm it will be here for the next vocoder V update (already internally tested, and yes it works fine.)
stay tuned!
best regards,