two-way synchronization accross a firewall fails

[Tim Harsch]

machine O is outside firewall, machine I is inside (machine names changed to
protect the innocent :-)

firewall allows ssh connections if inititiated from I to O, but not if the
other way.

both machines have an /etc/rsyncd.conf of:
[rt]
     path = /tmp/rsync_test
     comment = Test area

O runs rsync daemon, I initiates a rsync cammnad like
rsync -rvvv --delete --rsh=ssh O::rt /tmp/rsync_test

which works great, but when flipped and run on machine I, like so:
rsync -rvvv --delete --rsh=ssh /tmp/rsync_test  O::rt

we get
rsync -rvvv --delete --rsh=ssh /tmp/rsync_test O::rt
opening connection using ssh O rsync --server --daemon .
root at est.llnl.gov's password:
building file list ...
[sender] make_file(rsync_test,*,2)
[sender] expand file_list to 131072 bytes, did move
[sender] make_file(rsync_test/t,*,2)
[sender] make_file(rsync_test/core,*,2)
[sender] clearing per-dir .cvsignore exclude list
done
send_file_list done
send_files starting
rsync: connection unexpectedly closed (28 bytes read so far)
rsync error: error in rsync protocol data stream (code 12) at io.c(342)
_exit_cleanup(code=12, file=io.c, line=342): about to call exit(12)