When changing the password of a key where the primary key is offline and only a secret subkey is present, you get a confusing message:

gpg> passwd
gpg: Schlüssel 06E28F5FB5297489/06E28F5FB5297489: Fehler beim Ändern des Passwortes: Kein geheimer Schlüssel

but a password prompt comes up anyway.
This is because the error message is for the primary key, for the second one you do not get a message unless you e.g. abort at the password prompt:

gpg> passwd
gpg: Schlüssel 06E28F5FB5297489/06E28F5FB5297489: Fehler beim Ändern des Passwortes: Kein geheimer Schlüssel
gpg: Schlüssel 06E28F5FB5297489/037BFD4B2C571A9E: Fehler beim Ändern des Passwortes: Verarbeitung wurde abgebrochen

Instead of "Error changing passphrase:" a better phrasing here would be "Skipping:"

But maybe it is too difficult to determine the context of the output?