git diff-tree commit detail bug in 2.0.2 and 2.0.3

Using git diff-tree --stdin on 2.0.2 and 2.0.3 produces incorrect commit messages.

Here's an example to reproduce the issue:

bturner@ubuntu:/tmp$ git init --bare test.git
Initialized empty Git repository in /tmp/test.git/
bturner@ubuntu:/tmp$ git clone test.git
Cloning into 'test'...
warning: You appear to have cloned an empty repository.
done.
bturner@ubuntu:/tmp$ cd test
bturner@ubuntu:/tmp/test$ echo "Hello" > file.txt
bturner@ubuntu:/tmp/test$ git add file.txt
bturner@ubuntu:/tmp/test$ git commit -m "Initial commit"
[master (root-commit) c5e16f3] Initial commit
 1 file changed, 1 insertion(+)
 create mode 100644 file.txt
bturner@ubuntu:/tmp/test$ echo "World" >> file.txt
bturner@ubuntu:/tmp/test$ git commit -am "Second commit"
[master 9214ac7] Second commit
 1 file changed, 1 insertion(+)
bturner@ubuntu:/tmp/test$ git push origin HEAD
Counting objects: 6, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (2/2), done.
Writing objects: 100% (6/6), 446 bytes | 0 bytes/s, done.
Total 6 (delta 0), reused 0 (delta 0)
To /tmp/test.git
 * [new branch]      HEAD -> master
bturner@ubuntu:/tmp/test$ cd ../test.git/
bturner@ubuntu:/tmp/test.git$ git rev-list -1
--format="%H|%h|%P|%p|%aN|%aE|%at%n%B%n" 9214ac7
commit 9214ac79728424a971244c34432c6d948754198d
9214ac79728424a971244c34432c6d948754198d|9214ac7|c5e16f37164f1b7411685def64d7390775437f07|c5e16f3|Bryan
Turner|bturner@atlassian.com|1406539558
Second commit

bturner@ubuntu:/tmp/test.git$ /opt/git/2.0.3/bin/git diff-tree --no-renames --always --format="commit %H%n%H|%h|%P|%p|%aN|%aE|%at|%B%n" --root 9214ac79728424a971244c34432c6d948754198d commit 9214ac79728424a971244c34432c6d948754198d 9214ac79728424a971244c34432c6d948754198d|9214ac79728424a971244c34432c6d948754198d|c5e16f37164f1b7411685def64d7390775437f07|c5e16f37164f1b7411685def64d7390775437f07|Bryan Turner|bturner@atlassian.com|1406539558|Second commit

:100644 100644 e965047ad7c57865823c7d992b1d046ea66edf78 f9264f7fbd31ae7a18b7931ed8946fb0aebb0af3 M file.txt bturner@ubuntu:/tmp/test.git$ /opt/git/2.0.3/bin/git diff-tree --no-renames --always --format="commit %H%n%H|%h|%P|%p|%aN|%aE|%at|%B%n" --root --stdin --9214ac79728424a971244c34432c6d948754198d commit 9214ac79728424a971244c34432c6d948754198d 9214ac79728424a971244c34432c6d948754198d|9214ac79728424a971244c34432c6d948754198d|c5e16f37164f1b7411685def64d7390775437f07|c5e16f37164f1b7411685def64d7390775437f07|Bryan Turner|bturner@atlassian.com|1406539543|Initial commit

:100644 100644 e965047ad7c57865823c7d992b1d046ea66edf78 f9264f7fbd31ae7a18b7931ed8946fb0aebb0af3 M file.txt bturner@ubuntu:/tmp/test.git$

Running a git bisect between v2.0.1, which does not manifest this
issue, and v2.0.2 fingers the following commit:
bturner@ubuntu:~/Development/oss/git/git$ git bisect bad
c1b3c71f4b4571abb2b2a457122fd100dc9f7eb0 is the first bad commit
commit c1b3c71f4b4571abb2b2a457122fd100dc9f7eb0
Author: Jeff King <peff@peff.net>
Date:   Tue Jun 10 17:43:02 2014 -0400

    commit: convert commit->buffer to a slab

Bryan Turner