False alarms from git-fsck(1) about missing commits/trees pushed after the run started

I ran `git-fsck --full --verbose` on a bare Git repository which users
push to (over ssh).

It reports things like this:

    missing commit c7836745b13ce838439b3705d3c5c93bc0add6a6
    missing tree ef59d2bee486b6af5ae36eb9ff2e9de0d52f37ab
    missing commit 786315c755ac91d3a1ffc3d92679dda961035617

But actually these things aren't missing. They were just pushed to the
repo after the fsck run started.

Is this a known limitation of git-fsck, is it documented anywhere? If
it's not supposed to do this maybe there's a race condition somewhere
in it.