git merge no longer fast forwards

gistfile1.txt

I am using git version 1.7.9, built by me from git on Debian/testing.

I am on the Linux-2.5-stable tree.
Ie: git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
I just fetched after GregKH posted v3.2.3 was out.

$ git describe
v3.2.2

$ git merge-base v3.2.2 v3.2.3 | xargs git describe
v3.2.2

$ git merge --ff-only v3.2.3
fatal: Not possible to fast-forward, aborting.

BTW, after merging (without --ff-only), I got a merge commit with no changes on
the left side and all the v3.2.2..v3.2.3 changes on the right side (in gitk).
Running diff v3.2.3 shows no deltas. Running git show also has no deltas.