Revoking signature of GnuPG-key in seahorse

Hi all,

I subscribed to the fish-shell mailing list quite a while ago (https://sourceforge.net/projects/fish/lists/fish-users ) and frequently get
e-mails from the developer and maintainers.

On Feb 13 2020 I got an e-mail from David Adam which contained a PGP signed message together with the PGP signature.

I use thunderbird with enigmail and imported his public key. Furthermore I signed the key as I trust David Adam.
He had sent me the fingerprint before.

For the signing I used seahorse (GNOME front end for GnuPG) and checked “I want to be able to revoke the signature at another point in time”.

Nevertheless revoking doesn´t work (tab “trust”) because the button “revoke signature” is greyed out.

Does anybody know something about this?

Thanks a lot in advance.
Greetings.
Rosika :neutral_face: