Unable to edit custom field multiple choice options

When editing a custom field I want to change it from using a pre-existing set of multiple choice options, and instead create a new set of multiple choice options.
If I edit the field I can click the 'Option type' radio button to switch it from re-using an existing set to allow me to create a new set of options. I then create the new set of options, and save the changes.

However the changes are not saved and the field continues to re-use the previously defined set of options.

I was able to replicate this behaviour on the demo server at d46.demo.civicrm.org