Pasting numbers in customized world generation text fields does not enable "Defaults" button

The bug

When you paste numbers in the text fields of the customized world generation GUI on the last page (fourth), the "Defaults" button does not become enabled.

How to reproduce

1. Go to the fourth page (page with the text fields) of the customized world generation settings
2. Paste a number in one of the text fields
   The value has changed but the "Defaults" button is still disabled