Have two annoying clues:
2d Be contrary to ordinary procedure, and include many different groups 3,6
C _ T / _ E _ O _ S
and 24a Terrier shown by porter 8 _ I _ E _ A _ E
Well, that would mean that 14a Thoughtless broadcast knocked on the head 14
isn't featherbrained. Brained is definitely correct as knocked on the head but I can see why feather might be wrong - this would make it _ C _ T _ E _BRAINED