This happens when git merge is run to merge multiple commits that are
descendants of current HEAD (or are HEAD). We've hit this while updating
master to origin/master but accidentaly we called (while being on master):
$ git merge master origin/master
Here is a minimal testcase:
$ git init a && cd a
$ echo a >a && git add a
$ git commit -minitial
$ echo b >a && git add a
$ git commit -msecond
$ git checkout master^
$ git merge master master
Fast-forwarding to: master
Already up-to-date with master
Merge made by the 'octopus' strategy.
a | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
$ git cat-file commit HEAD
tree
eebfed94e75e7760540d1485c740902590a00332
parent
bd679e85202280b263e20a57639a142fa14c2c64
author Michał Kiedrowicz <michal.kiedrowicz@gmail.com>
1329132996 +0100
committer Michał Kiedrowicz <michal.kiedrowicz@gmail.com>
1329132996 +0100
Merge branches 'master' and 'master' into HEAD
Signed-off-by: Michał Kiedrowicz <michal.kiedrowicz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>