Weird behavior with git grep --recurse-submodules

Hi guys,

I work with submodules and use git grep a lot.

I noted that when it is invoked used with --recurse-submodules, the result is not as expected for the submodules. I get submodules results as if no files were modified (like --cached option) although I would expect results taking into account the modifications.

Expected behavior:
git grep --recurse-submodules string:
- git grep string // search into main repo
- for each submodule, git grep string // search into submodule

Actual behavior:
git grep --recurse-submodules string:
- git grep string // search into main repo
- for each submodule, git grep --cached string // search into submodule

Do you get the same behavior? Am I doing something wrong? Was I understandable :-)? Is it a bug?

git --version: git version 2.22.0 uname -a: Linux daniel 5.1.15-arch1-1-ARCH #1 SMP PREEMPT Tue Jun 25 04:49:39 UTC 2019 x86_64 GNU/Linux

Thanks Daniel