git apply does not work from within the local checkout of an unrelated git repository

As freshly documented at http://drupal.org/patch/apply

git apply will fail to do anything when used within a local checkout of a git repository (other than the one for the project the patch is made for), such as if you are patching a module that is within a site that is in Git version control. Use patch -p1 < path/file.patch instead.

Background:
Here's a fun one. A patch that i apply with git apply has no effect whatsoever. When i use patch -p1 it works just fine
17:19 mlncn: History: this is a patch that i rolled at one point.
17:20 mlncn: i haven't noticed yet anywhere in the documentation of git apply that it will ignore anything it thinks you already have-- because i don't have it, views has been updated twice since i applied the patch.
17:27 mlncn: ... or maybe git apply just doesn't like the patch for some reason-- third one on this comment, if anyone has the latest views to try it on: http://drupal.org/node/817748#comment-4265772
17:27 Druplicon: http://drupal.org/node/817748 => Sort by Book Hierarchy does not exactly repeat book hierarchy => Views, book data, normal, reviewed & tested by the community, 14 comments, 4 IRC mentions

extremely weird. Running it gave me no output at all, and patch -p1 < worked fine
git apply does not have the < right? (Answer: works either way, with or without)
17:34 mlncn: hmm- i have this in a larger repository. I'll try some other random patch
17:34 mlncn: i have git version 1.7.1 btw
is there no output or no patched file? git apply doesn't report anything on success
17:36 mlncn: no output and the file is not patched
17:36 mlncn: it's all in version control (a site) and no change
17:36 mlncn: in the diff
17:36 mlncn: nor in the file, i checked that way too
17:37 mlncn: that patch majorly changes the file, not like i could miss it
git apply does not patch anything at all when it detects a conflict but in that case, it reports that

git apply works- it applies in a freshly downloaded views not in a repository
also applies in a separate git clone of views

it is supposed to work when it's in a random other repository, right?

git apply is not working when used from within my local checkout of the dgd7 site

i think it's official: git apply doesn't even try if it's already in a repository (other than the one for the project the patch is for)

18:07 mlncn: git apply --apply --verbose ../1113624-use-views-cache-loader-in-export-ui.patch
18:07 mlncn: no output
18:07 mlncn: rm -rf ../.git/
18:07 mlncn: git apply --apply --verbose ../1113624-use-views-cache-loader-in-export-ui.patch
18:07 mlncn: Checking patch plugins/export_ui/views_ui.class.php...
18:07 mlncn: Applied patch plugins/export_ui/views_ui.class.php cleanly.
18:08 mlncn: I'm documenting this. Not that i understand it, and i've read the git apply man file, but giving the next me a warning.