Bugs ignoring submodules?

Hi,

I'm trying to format patches ignoring changes in the submodules, and
so far everything I've tried is failing, which I think points to
multiple bugs. I'm using 1.6.5.2.

First I tried:
% git format-patch --ignore-submodules

That ignores the submodules, all right, but still generates an empty
patch, just like 'git log' shows no diff.

Then I tried:
% git log <committish> -- $(git ls-files -x <submodule>)

But the submodule is still listed:
% git ls-files --exclude=common | grep ^common
common

These are bugs, right? Is there some other recommendation?

-- 
Felipe Contreras