AllPosts page: contradiction in filtering by Category and category assigning to the post

[antonrinas]

STEPS TO REPRODUCE:

1. Log in as administrator.
2. Go to Posts->Categories.
3. Add category: Name - "Test category", Slug - "test-category".
4. Add category: Name - "Test subcategory", Slug - "test-subcategory", Parent - "Test category".
5. Go to AllPosts page.
6. Add new post: Title - "Test post", assign it to "Test category".
7. Add new post: Title - "Test post for subcategory", assign it to "Test subcategory".
8. Go to AllPosts page.
9. Filter posts by category "Test category".

EXPECTED RESULT:
Post "Test post" is presented as a result of filtration.
ACTUAL RESULT:
Posts "Test post", "Test for subcategory" is presented as a result of filtration. If to follow this logic, post "Test post for subcategory" had to be assigned to "Test subcategory" and automatically to parent category in the moment of creation.
See attachment.