gpg generates malformatted packet

[Ulf Möller]

If I run

echo "Guten Tach." | gpg -ca --s2k-mode 0 

(which, according to OpenPGP, is not allowed), GnuPG 1.0.0 prints a
warning, but then proceeds to encrypt the input. The encrypted message
contains a correct compressed packet, but the literal packet inside is
malformatted.

According to the packet header, it is an old-format indeterminate
length packet, but that is follwed by two length bytes. This does not
happen with the other S2K modes.