When I request partial user data, back button no longer works

You mean that in the modal dialog requesting permissions and having [OK] and [Cancel] buttons, the Back button on the remote "does nothing" (or angrily beeps, whatever) - instead of what you find logical, work as Cancel ?

If that describes your case correct, then it's just a bad/clumsy UX of the component. Nothing you can do, it's for RokuCo to enhance

Yeah, that sounds like it. So this is the way it works for everyone? I was wondering if something with my message port was messed up or.. a setting was off. 

But to confirm: The back button does not logically work as "Cancel" in the modal dialog requesting user permission intentionally and there's nothing I can do about it?

The dialogs of roChannelStore are entirely handled by the firmware and you only get the final result - i'd consider this matter of security (so one could not meddle with the purchase process by inserting misleading product naming/pricing). So no, i don't see anything you could've done differently

I haven't tried it myself, but I'd expect it to act the same for everyone.  I noticed this in this in the "Roku Channel Certification Checklist v2.0":

7.17 - The back button behaves as expected and returns the user to previous screen and/or state

Sounds like a case of do as we say, not as we do.  😄

-JT