Certification signatures on subkeys

[Mihai Ibanescu]

Hi,

I noticed something strange on a key I imported:

http://pool.sks-keyservers.net:11371/pks/lookup?search=0x10FA4CD1&op=vindex

As you can see, the subkey has certification (type 0x10-0x13) signatures on
its subkey.

At least the way I read RFC4880, the only types of signatures that should be
present on a subkey are key binding or revocation signatures.

Am I missing something?

If this is a valid scenario, can someone point me to a spec with a description
of how the certification signature is hashed in this case? RFC4880 indicates
only how it gets hashed when attached to a User ID or User Attribute case.

Thanks!
Mihai

PS apologies if this doesn't belong to gnupg-devel.