[5.6.12]: Maintain hierarchy setting broken for new entries

[thupsi]

What happened?

Description

I have a categories field with the setting maintain hierarchy enabled. Since upgrading to 5.6.12, on entry creation the field is populated with all categories from the selected category group.

Even worse, when, for testing purposes, I changed the field type to an entries field it seemingly tried to populate with all the entries. I say 'seemingly' because the entry form then crashed.

Steps to reproduce

1. Have an categories or entries field in your entry layout, with maintain hierarchy enabled.
2. Create a new entry.

Expected behavior

The field should be empty.

Actual behavior

The field is populated with many categories/entries.

Craft CMS version

5.6.12

PHP version

No response

Operating system and version

No response

Database type and version

No response

Image driver and version

No response

Installed plugins and versions

[brandonkelly]

Thanks for reporting! This was also fixed by the #16920 fix in Craft 5.6.13.