git pull fails with http urls?

I've noticed a problem with pulling http urls. I can clone them fine:

  git clone http://www.gnome.org/~alexl/git/gio.git/

and I can pull with:

  git pull

which works as expected however if I try:

  git pull http://www.gnome.org/~alexl/git/gio.git/

it fails with:

  error: pick-rref: HEAD not found
  No such ref HEAD at http://www.gnome.org/~alexl/git/gio.git/

The HEAD file is there at http://www.gnome.org/~alexl/git/gio.git/HEAD
and:

  git pull http://www.gnome.org/~alexl/git/gio.git/ master

works. It seems git just doesn't want to see/understand the HEAD file?

Is the above supposed to work or is something wrong with the above
commands? I see this with git 1.5.2.3 and 1.5.3, google suggests this
might have worked with 1.4.x and broke in 1.5...

Regards,

Richard