The patch to the specs would be this:
The three data items hashed for document signatures need to - mirror the values of the Literal Data packet. For detached - and cleartext signatures 6 zero bytes are hashed instead. + mirror the values of the Literal Data packet. Note that for a + detached signatures this means to hash 6 0x00 octets and for a + cleartext signature this means to hash a 't' followed by 5 0x00 + octets.