[Possible bug] diff-tree --stat info does not count copies

While testing qgit with the new rename/copy support  I found this
(possible) bug playing on git tree.

$ git-diff-tree -r --stat 6973dca
6973dcaee76ef7b7bfcabd2f26e76205aae07858
  Makefile                      |    2
 diff-files.c                  |  212 +----
 diff-lib.c                    | 1862 ++---------------------------------------
 diff.c                        | 1795 ++++++++++++++++++++++++++++++++++++++++
 diff.h                        |    7
 t/t1001-read-tree-m-2way.sh   |    2
 t/t1002-read-tree-m-u-2way.sh |    2
 7 files changed, 1929 insertions(+), 1953 deletions(-)

$ git-diff-tree -r --stat -C 6973dca
6973dcaee76ef7b7bfcabd2f26e76205aae07858
  Makefile                      |    2
 diff-files.c                  |  212 +----
 diff-lib.c                    | 1862 ++---------------------------------------
 diff-lib.c => diff.c          |    0
 diff.h                        |    7
 t/t1001-read-tree-m-2way.sh   |    2
 t/t1002-read-tree-m-u-2way.sh |    2
 7 files changed, 134 insertions(+), 1953 deletions(-)

IMHO the bug is

   "diff-lib.c => diff.c          |    0"

instead of

   "diff-lib.c => diff.c          |    1795"

because, after the patch applied, in the repository we have
1953-1929=24 lines of code more, not 1953-134= 1819 less.

Thanks
Marco