Not prorating upgrade with Pro-Rating with Multiple Memberships disabled

We ran into an issue with Membership Pro 2 add-on Pro-Rating with Multiple Memberships disabled.

A member upgraded their account from a Basic membership to Expert but they were not prorated. Instead Expert membership was added to their membership list... even though we had Multiple Memberships disabled.

After some playing around, we enabled Multiple Memberships and set the Upgrade Paths pro-rating settings individually.

While we have a work around, wanted to share with everyone in case they run into the same situation.

It would also be a cool feature on the back end to be able to prorate a refund as a customer care tool for an irate customer. It would be nice to be a simple button instead of having to track it down in PayPal calculate the prorated refund ourselves.