Field group is not added if group was deleted

Steps:

1. Add custom block to configuration using nested attributes.
2. Create Landing page.
3. Add this block.
4. Open block settings.
5. Add two new instances of the field group (three in total). Submit.
6. Delete the first field group from the top. Submit.
7. Add third field group again. Submit.
8. Open block settings.

Actual result: Two field groups are present.
Expected result: Three field groups are present.