Saltstack custom execution module does not work with file_roots on remote git

Question

I created a custom execution module. Salt will see it if file_roots is on local and the module is placed in /srv/salt/_modules. If I redefined file_roots to remote git (setting up fileserver_backend to git), and put this module under file_roots/_modules. I verified the new module is on salt master in /var/cache/salt/master/gitfs/hash/_modules. This means salt actually replicated git to local cache. But for whatever reason, salt does not load it.

I ran saltutil.sync_all and it does not show any module.

Is there anyone actually who can help me to validate this ? I am thinking this might be a bug.