Adding a new field assigns the field to the last fieldset section

[kaidesu]

Describe the issue

When adding a new field with multiple sections present, the field is always added to the last section.

To reproduce

1. Create a fieldset
2. Add a new section
3. Go to the first section
4. Add a field
5. The field is added to the last section

Expected behavior

The field to be added on whatever section is currently active

Version and browser

Version: v6.0.0 Beta 9

Bug report checklist

• I have filled out as much information as I can
• I have detailed how the issue can be reproduced
• I have searched for existing issues and to the best of my knowledge this is not a duplicate