Search files with spaces by filename field

(from github.com/jay-cyrb)
I have 2 files: ‘мой_документ.doc’ and ‘мой документ.doc’. Both of them are indexed. Then I search by
filename:“мой_документ.doc”
I get results which contains link to my_document.doc .
But if I search by
filename:“мой документ.doc”
search result page is empty!
Why FESS can’t found file ‘мой документ.doc’ ? Maybe this problem with the space in filename?

(from github.com/marevol)
You can check indexed documents at Admin Search page.

(from github.com/jay-cyrb)
I try search this file at Admin Search by ‘*’ query and find it. But I still can’t find it with query
filename:“мой документ.doc”
Result page:
По запросу - filename:"мой документ.doc" - совпадений не найдено.

(from github.com/marevol)
filename:"мой документ.doc" is a phrase query.
Could you try filename:мой\ документ.doc?

(from github.com/jay-cyrb)
I try filename:мой\ документ.doc and get same result, i.e. nothing was found.