"Defaults" button of customized world generation always disables when "Customize" is clicked

The bug

When you change some settings in the customized world generation settings, then click the "Done" button and then the "Customize" button again the "Defaults" button is disabled again.

How to reproduce

1. Open the customized world generation settings

2. Change a value
   The "Defaults" button should be enabled

3. Click the "Done" button

4. Click the "Customize" button again to edit the settings
   The "Defaults" button is disabled but the value is still changed