In Bug 78, shortkey points out:
authorMike Frysinger <vapier@gentoo.org>
Sat, 16 Apr 2005 04:56:11 +0000 (04:56 -0000)
committerMike Frysinger <vapier@gentoo.org>
Sat, 16 Apr 2005 04:56:11 +0000 (04:56 -0000)
commit5ba5f4d2e72791fef3065a2221a3d386e0d17982
tree7bf8b5d352ccdbd0bd3ed39d38fcb8fd6eb8663e
parentb31566ef3273ad32a1e318d9293e44cc50d07b91
In Bug 78, shortkey points out:

If you run `grep -h . file1 file2 file3 ...`, the output is not prefixed
with the filename.  If you run `grep -h . file1` however, the filename
will incorrectly prefix the output.
findutils/grep.c