Restoring PGPPublicKeyRing from bytes discards additional PGPPublicKeys

Hi!

In my project I wrote code to generate an elliptic curve key ring. A key
ring consists of an ECDSA key pair used for signing and a second ECDHE
key pair used for encryption.

When I serialize the key ring and create a new instance from bytes, the
key ring only contains the first key pair. The second one gets discarded.

PGPPublicKeyRing ring = ...
byte[] bytes = ring.getEncoded(true);
PGPPublicKeyRing parsed = new PGPPublicKeyRing(bytes);

By stepping through the execution, I figured, that the cause of this
issue is probably, that the constructor of PGPPublicKey only checks for
the packet tag of a PUBLIC_SUBKEY, while the second key has the packet
type PUBLIC_KEY.
See
https://github.com/bcgit/bc-java/blob/master/pg/src/main/java/org/bouncycastle/openpgp/PGPPublicKeyRing.java#L114

I suspect, that the constructor of PGPPublicKey is probably doing the
right thing, but the question is, what did I wrong then when creating my
key ring / why does the getEncoded() method use PUBLIC_KEY as packet tag
instead of PUBLIC_SUBKEY?

I added the subkey as follows:

PGPKeyRingGenerator ringGenerator = new PGPKeyRingGenerator(
    PGPSignature.POSITIVE_CERTIFICATION, certKey,
    userId, calculator,
    hashedSubPackets, null, signer, encryptor);

PGPKeyPair subKey = generateKeyPair(subKeySpec); // Generates a PGPKey pair
ringGenerator.addSubKey(subKey);

My code can be found here:
https://github.com/vanitasvitae/pgpainless/blob/master/src/main/java/org/pgpainless/pgpainless/key/generation/KeyRingBuilder.java

Paul