gpg: mdc_packet with invalid encoding

I'm attempting to decrypt a signed message.

When decrypting using the browser it does so successfully with no error messages and additionally displays a "signed by XXX" green box, indicating it's also signed.

However when I run `keybase decrypt --signed` from the command line:
1. there is no output, so I paste in the encrypted PGP message, which is encrypted by version "Keybase OpenPGP JS 0.0.1", with comment "https://keybase.io/crypto".
2. At this point it prompts me saying "You need a passphrase to unlock the secret key for user ...." so I type it in.
3. On entering the passphrase there is again no output, so I paste in the encrypted message again.
4. The command-line utility then outputs the decrypted message successfully, and shows the following warning and error output right below the decrypted message:

```
warn: gpg: encrypted with 4096-bit RSA key, ID 85E8BBEBF2A2BA04, created 2014-03-07
warn: "keybase.io/asim "
warn: gpg: Signature made Fri 07 Mar 2014 11:49:32 GMT
warn: gpg: using RSA key B97A77F5E32E0A17
warn: gpg: Good signature from "keybase.io/inglesp "
warn: Primary key fingerprint: 7B50 BD7B 9413 E347 ECFA E03E 046A DEFC 000B 7381
warn: Subkey fingerprint: 8769 1236 8BD5 EF97 41BD E673 B97A 77F5 E32E 0A17
warn: gpg: mdc_packet with invalid encoding
warn: gpg: decryption failed: invalid packet
error: `gpg` exited with code 2
```

My guess is that the message's integrity is valid, but the warning output is very scary and I don't understand it.

Start by reproducing the reported `keybase decrypt --signed` flow with the supplied encrypted message and compare its output with browser decryption. Inspect how the CLI handles gpg warnings and exit code 2. Done means determining whether the message is successfully verified and decrypted, and defining the expected behavior for the invalid-packet warning.

Written by the indexing model from the issue text.