Contribution pages UI failes to configure membership_recur with price set

LOGGING THIS BUT I NEED TO DO MORE TESTING AS GETTING INCONSISTENT RESULTS

In order to configure a membership price set to work as a recurring with Authorize.net you need to

1) configure the membership type in it (let's stick with one) to be optional renew
2) set the contribution page to use a price set on the membership tab
3) set the contribution page to be recurring

If you fail to do the 3rd of these then the contribution page will say it is renewing - but not actually create a recurring contribution. (certainly this is the case with Authorize.net)

I think at one point I figured out a combination of clicks that made this possible in the UI - but now I don't seem to be able to ....