Write screen does not honor category hierarchy

[MtDewVirus]

When writing a new post, selecting categories, and saving, All Categories no longer honors the category hierarchy for children that aren't selected.

Steps to reproduce:

1. Create Categories Parent1 (with Child1 and Child2), Parent2, Parent3
2. Write a new post
3. Select Parent1, Child1, Parent2 as categories
4. Save the post
5. Child2 will appears at the bottom of the All Categories list as if it was a parent category.

Screenshots attached.

[mrmist]

Dup of #6920