In Customized settings' page 1, 'Previous Page' button is unlocked after resetting defaults

The bug

When creating a customized world, the Previous Page button shows itself unlocked after resetting the settings. But the reset drives you to the first page, where the button shouldn't be unlocked since there isn't any page before it. After clicking it, it becomes locked again, and nothing happens.

How to reproduce

1. Change some settings in the Customized creation menu.
2. Reset them to the default, using the Defaults button.
3. Look at the Previous Page button. It's unlocked, but in page 1.
4. Click on it - nothing happens.