workaround for https://github.com/dotcloud/docker/issues/3877

docker-save.sh

#!/bin/bash -ex
# Wrapper for 'docker save' fixing,
# https://github.com/dotcloud/docker/issues/3877
# In addition: this script will always save exactly one image (possibly
# multiple tags).

IMAGE=$1
TARGET=$2
NAME=`echo $IMAGE | awk -F':' '{print $1}'`
ID=`docker inspect $IMAGE | python -c "import sys,json; print json.load(sys.stdin)[0]['id']"`
TAGS=`docker images --no-trunc | grep $ID | awk '{print $2}'`
DIR=`mktemp -d --suffix=-docker-save`
pushd $DIR

docker save $ID > $TARGET

# Write the 'repositories' file containing all tags pointing to this image.
echo $TAGS | python -c "import sys, json; tags = raw_input().split(); h = {'$NAME': {tag: '$ID' for tag in tags}}; print json.dumps(h)" > repositories
cat repositories

# GNU tar fails, where python's tarfile succeeds.
# https://github.com/dotcloud/docker/issues/3877#issuecomment-37086616
python -c "import tarfile; f=tarfile.open('$TARGET', 'a'); f.add('repositories'); f.close()"

popd
rm -rf $DIR

Would you mind to add a license (comment) to that file? e.g. MIT-Lincensed or something?

BTW:
You need to change line from id -> Id (uppercase i)