[RFD] git update-index --remove frotz --add frotz expected behaviour?

I'm a bit stumped by update-index' behaviour when calling --remove and 
--add on the same file in that order:

$ touch frotz
$ git update-index --add frotz
$ rm frotz
$ git status -s
AD frotz
$ git update-index --remove frotz --add frotz
$ echo $?
0
$ git status -s
$

Notice that update-index doesn't complain that I'm trying to add a file 
that doesn't exist, and it's returning with 0.

Is this expected behaviour? Shouldn't I get some sort of error message 
telling me that I'm trying to add a file I've just removed? Compare:

$ touch xyzzy
$ git update-index --add xyzzy
$ rm xyzzy
$ git update-index --remove xyzzy
$ git update-index --add xyzzy
error: xyzzy: does not exist and --remove not passed
fatal: Unable to process path xyzzy

Can anyone explain this to me?