Changes to Input Formats not saving: Default instance field is required When trying to make any changes to any text format, when I click "Save" Drupal returns an error message: "Default instance field is required." and the changes are not saved. Screenshot: http://awesomescreenshot.com/0ff38my7f7 (Drupal version 7.30.)

Can anyone suggest what could be causing this?
I was getting this error because of qTip filter (https://www.drupal.org/project/qtip) which had a required field that wasn't visible on the text format page because qTip filter wasn't selected. The required field was still part of the form (visible in source) even though it was invisible in the rendered page.