git fetch with GIT_SSH fails with "The remote end hung up unexpectedly"

[Gert Palok <gert_p@ut.ee>]

At my work I have to use an intermediate gateway to ssh to the outer
world. I have set up private-public keys to allow easy connection:
ssh gateway ssh user@outside

Now, I want to fetch from outside repo, so I created a GIT_SSH wrapper:

#! /bin/bash

LOG="/path/to/git-ssh-wrapper.
log"
HOST="$1"
COMMAND="$2"

echo host: $HOST >>"$LOG"
echo command: $COMMAND >>"$LOG"
echo exec: ssh gateway ssh "$HOST" $COMMAND >>"$LOG"
ssh gateway ssh "$HOST" $COMMAND

And ran:
$ GIT_SSH="/path/to/git-ssh-wrapper" git clone ssh://user@outside/path/to/repo
Initialized empty Git repository in /path/to/local-repo/.git/
warning: You appear to have cloned an empty repository.
$ fatal: The remote end hung up unexpectedly

And again just to be sure:
$ GIT_SSH="/path/to/git-ssh-wrapper" git fetch origin
$ fatal: The remote end hung up unexpectedly
fatal: The remote end hung up unexpectedly

Now, the log says:
host: user@outside
command: git-upload-pack '/path/to/repo'
exec: ssh gateway ssh user@outside git-upload-pack '/path/to/repo'

When I ran the command from shell I got:
$ "$GIT_SSH" user@outside "git-upload-pack '/path/to/repo'"
0000

And the connection was kept open (waiting for input, got protocol
error after entering something)

Local environment: Windows Vista 32-bit, cygwin 1.7
Local git version (installed by cygwin): 1.6.4.2
Remote git version: 1.6.4.4

What might be the cause(s)? Have there been compatibility breaking
protocol changes between those version?

--
Gert Palok