If a gpg keyring contains a primary key that is marked with only the "certify"
usage flag (0x01), then running gpg --with-colons --fixed-list-mode --list-key
fails to properly set field 12 ("key capabilities"). It should read 'cC', but
instead, it is the empty string.
gpg --export | gpg --list-packets contains the correct information in the "key
flags" line, however.