Understood.
Unfortunately, the customer experience I'm after (the "show member pricing" behavior) is requiring me to also add member pricing info to the menu option area (I hear you, it shouldn't work that way) to get the member pricing *actually* applied at checkout (since the checkbox isn't working properly). Again, I'm not sure why this is happening the way it is...on our site, login is required to even see the store tab, and checking the member-pricing checkbox throws the "login" error (even though I'm obviously already logged in), so, to get member pricing applied I added the label and price to the Member Pricing menu option (leaving the BuyNow setting on "Show Member Pricing") and (like magic) the member price is automatically being applied. Yes, the checkbox is still there, but serves no function since member pricing has already been automatically applied.
Most certainly not the solution you had intended for this pretty-typical use case, but it works (as long as my customers aren't confused by the checkbox and login message...which I can hack per your instructions)
So, I'm not sure where we go from here...maybe there's a bug in the member pricing if the store page is only visible to registered users.?.?