How do I turn off the "Contribution amounts section" for a membership only contribution page?
I see the same thing on Drupal/CiviCRM 4.7.18 - but it looks like the checkbox only gets checked again -> when you go into the Config. That is you can still uncheck it and Save it and have a Membership only Contribution form with no additional amounts. For some reason it defaults to ON now on edit of the contribution form config. Definitively a bug - and a regression [this was for sure working previously].