git subtree oddity

[Thomas Taranowski <tom@baringforge.com>]

I'd like to have the following configuration:

/myproject.git
|__/upstream_dependency -- Points to a remote library git repo
|__/project_source -- local project source


I issue the following commands to pull in the upstream dependency as a
subtree of the myproject.git repo:

git remote add upstream git://gnuradio.org/gnuradio
git fetch upstream
git checkout master
git subtree add -P upstream upstream/master

Now, my expectation is that I would have the following:

/myproject.git
|__/upstream_dependency -- Points to a remote library git repo
|____< all the upstream files are present here, as expected >
|__/project_source < this is still intact, as expected >
|__< all the upstream files are present here. wtf?>

My question is, why does "subtree add" pull in all the subtree files
into the root of the repo, and not just into the specified subtree
prefix?

#
# Here's an excerpt of what I see:
#
$:~/scratch/myproject.git$ ls
AUTHORS         gr-comedi               gr-utils
cmake           gr-digital              gr-video-sdl
CMakeLists.txt  gr-fcd                  gr-vocoder
config.h.in     gr-fft                  gr-wavelet
COPYING         gr-filter               gr-wxgui
docs            gr-howto-write-a-block  README
dtools          gr-noaa                 README.building-boost
gnuradio-core   gr-pager                README.hacking
gr-analog       gr-qtgui                README-win32-mingw-short.txt
gr-atsc         gr-shd                  upstream <---- the subtree directory
gr-audio        gr-trellis              volk
gr-blocks       gruel
grc             gr-uh

#
# Also, those same files are in the upstream subtree directory as well
(as expected)
#
$:~/scratch/myproject.git$ ls upstream
AUTHORS         grc                     gruel
cmake           gr-comedi               gr-uhd
CMakeLists.txt  gr-digital              gr-utils
config.h.in     gr-fcd                  gr-video-sdl
COPYING         gr-fft                  gr-vocoder
docs            gr-filter               gr-wavelet
dtools          gr-howto-write-a-block  gr-wxgui
gnuradio-core   gr-noaa                 README
gr-analog       gr-pager                README.building-boost
gr-atsc         gr-qtgui                README.hacking
gr-audio        gr-shd                  README-win32-mingw-short.txt
gr-blocks       gr-trellis              volk