rebase with unknown -s parameter discards commits

git version: 2.5.0
Archlinux

Hi,

'git rebase -s nonsense master' gives an error message but still changes 
the branch.

$git rebase -s nonsense master topic
First, rewinding head to replay your work on top of it...
/usr/lib/git-core/git-rebase--merge: line 70: git-merge-nonsense: 
command not found
Unknown exit code (127) from command: git-merge-nonsense 
3cf5c040ccda670cc103184a6d7e03fc20293b81^ -- HEAD 
3cf5c040ccda670cc103184a6d7e03fc20293b8

And topic is the same as master now.

If I try to continue
$git rebase --continue
Already applied: 0001 Topic
All done.

But still topic is the same as master.

-----------------------------------------------------
topic and master was created with these commands:

$git init
$echo orig > text
$git add text
$git commit -m Orig

$git checkout -b topic
$echo topic > text
$git commit -am Topic

$git checkout master
$echo master > text
$git commit -am Master

$git rebase -s nonsense master topic
$git rebase --continue

$git log --oneline
04d7f1d Master
0ac994c Orig