count of taxonomy parent must be sum of count all childs

hello.
i have created a view for searching documents with facets blocks that i have activated them to display in this view page.
first i wanna discribe the structure of my content type named document.
it containt:
- title
- file (pdf)
- index field (taxonomy that i named index document with more than one level)
i have configured my facet display with Expand hierarchy so display parent and childs.
so the problem is in my taxonomy parent widget count, in the normal case count parent taxonomy must be the sum of count all childs but its not!
ok there is an example of my widget:

Filter by document index:

- Index1 (1)
- Index1.1 (1)

note: i have assigned a node to Index1, and an other node to Index1.1 so result must be like this:

- Index1 (2)
- Index1.1 (1)

note2:
i have uploaded a screenshot for more explanation.