Compare the output of:
gpg --with-colons --list-secret-keys
gpg --with-colons --list-secret-keys .
The first form (without a matching argument) fails to print the key capabilities
in field 12. The second form (matching any user ID that contains a dot) prints
the key capabilities in field 12.
I believe that the first form *should* print the key capabilities, to bring it
in line with the behavior shown by the more commonly-used --list-keys.