Unknown signature subpacket: 33, GnuPG 2.1.15

I am currently migrating to a new GPG key, so I wanted to revoking my proofs and then attach my new key.

My system now by default uses GnuPG 2 (version 2.1.15, to be exact). Trying to revoke the proofs spits out the error message "Unknown signature subpacket: 33". That I could fix by replacing "gpg" by "gpg1", i.e. by using the old GnuPG version.

However, adding my new key, created with GnuPG 2, does not work either, with the error message "Unknown signature subpacket: 33". And there, creating the armored export with gpg1 doesn't help either. So now I'm stuck with an empty keybase identity at the moment.

Start by reproducing proof revocation and new-key attachment with GnuPG 2.1.15, then compare the behavior with gpg1 using the issue's reported inputs. Trace where the "Unknown signature subpacket: 33" error is surfaced; done means both operations handle the GnuPG 2-generated key without leaving the Keybase identity empty.

Written by the indexing model from the issue text.