confusion with git diff-tree output

Hi all,

I've been struggling with trying to figure out how to make diff-tree
output the actual files changed.  Below is the output when I run
diff-tree on a given commit.  It reports that the directory is
modified, rather than that a single file within that directory is
modified.  I can find out what *file* was modified by running
diff-tree -p --raw, which gives me output similar to what I expected
from a plain old diff-tree.  Is there a flag that will make diff-tree
give this information?

As background, what I really want is --name-only, which rarely reports
the files modified, instead reporting the directories as modified, and
I've been struggling to figure out what is going on.  The
documentation seems to imply that the --raw diff output will report
modified files, and I haven't found anything indicating when it would
report the directories containing the modified files instead.

Thanks!
David

$ git diff-tree fd99a198222c14cf42fee82087a13467ff4a8205
fd99a198222c14cf42fee82087a13467ff4a8205
:040000 040000 8cdb796ea801da99c34d8f60045d8eb08fbb0e41
66b67ea1763799c0b2ac01f6803177ca870f6544 M	Iolaus

$ git diff-tree fd99a198222c14cf42fee82087a13467ff4a8205 -p --raw
fd99a198222c14cf42fee82087a13467ff4a8205
:100644 100644 dab4c531f3f69f08e5dc202ad8b6dfad9e8855fe
0e3f305e641a6440bb478765dfcd089e0420c155 M	Iolaus/Lcs2.hs

diff --git a/Iolaus/Lcs2.hs b/Iolaus/Lcs2.hs
index dab4c53..0e3f305 100644
--- a/Iolaus/Lcs2.hs
+++ b/Iolaus/Lcs2.hs

(changes cut)