git rebase --preserve-merges seems to not work

  In order to push changes to our master branch, one has to have pulled 
first.  We pull with the --rebase option.  It works great except for 
merge commits.

I discovered 'git rebase' has a --preserve-merges option.  I assumed it 
would allow me to rebase my merge commit on top of others' changes 
pushed to our central master branch.

Unfortunately, I can't seem to make it work.  Does anyone have thoughts 
on what I'm doing wrong?

My session is below.

Thanks!

Josh


$ git init

$ echo a > a
$ git add a
$ git commit -m a
$ git tag a

$ echo b > b
$ git add b
$ git commit -m b

$ echo c > c
$ git add c
$ git commit -m c
$ git tag c

# Note the hierarchy is simple: a <- b <- c
$ git lg --all
* d132c87 - (c) c
* 4a88fd1 - b
* b576660 - (a) a


# Create the hierarchy: a <- d
$ git checkout a
Note: checking out 'a'.

$ echo d > d
$ git add d
$ git commit -m d
$ git tag d

$ git lg --all
* 6abf527 - (HEAD, d) d
| * d132c87 - (c) c
| * 4a88fd1 - b
|/
* b576660 - (a) a


# Wanting to merge my branch back to my local master to push to the server.
$ git checkout a
$ git merge --no-ff c
Merge made by recursive.
  b |    1 +
  c |    1 +
  2 files changed, 2 insertions(+), 0 deletions(-)
  create mode 100644 b
  create mode 100644 c
$ git tag bc-merge


# Commit 'd' is something I would pull --rebase from the server before I 
push.
$ git lg --all
*   472fd93 - (HEAD, bc-merge) Merge commit 'c' into HEAD (3 seconds ago)
|\
| * d132c87 - (c) c (2 minutes ago)
| * 4a88fd1 - b (2 minutes ago)
|/
| * 6abf527 - (d) d (2 minutes ago)
|/
* b576660 - (a, master) a (3 minutes ago)


# Here is the rebase with the --preserve-merges option.
$ git rebase --preserve-merges d
Rebasing (n/3)
Successfully rebased and updated detached HEAD.

# Of course, bc-merge is an orphaned branch.  Its changes got replayed 
on top of 'd'.
# Note the merge commit with the description "Merge commit 'c' into 
HEAD" is missing.
$ git lg --all
* 2c93a8a - (HEAD) c (11 seconds ago)
* 2b98bc6 - b (11 seconds ago)
* 6abf527 - (d) d (3 minutes ago)
| *   472fd93 - (bc-merge) Merge commit 'c' into HEAD (74 seconds ago)
| |\
|/ /
| * d132c87 - (c) c (3 minutes ago)
| * 4a88fd1 - b (3 minutes ago)
|/
* b576660 - (a, master) a (4 minutes ago)