Backlinks to root item of a document

Hello,
I want to see backlinks to the root item of a document.

For example, when I link a child item of document A from document B, I can see backlinks for child item when I zoomed into that item.
But if I link document A itself from document B, backlinks list not show up.
(However when I zoom in and out at any child item in document A, I can see backlinks to document A. Is it a bug or intended behavior?)

Environment

Chrome 85 in Windows 10, same behaviour in latest iOS app in iOS 13.5


Sorry for my bad English.
Thank you.