“Why is a ghost such a messy eater?”/“Because he is always a goblin.”

A popular Halloween riddle about ghosts and goblins is:
 
Q: Why is a ghost a messy eater?
A: Because he is always a goblin.
   
The joke has been cited in print since at least 1997.
 
 
Google Groups: maus.talk.english
Halloween Jokes
Karl-Heinz Wachtendorf
11/2/97
(...)
Q. Why is a ghost such a messy eater?
A. Because he is always a goblin.
 
30 October 1998, The Star Democrat (Easton, MD), “Spooktacular Fun,” pg. 7B, col. 3:
Q. Why is a ghost such a messy eater?
A. Because he is always a goblin.
     
Google Groups: alt.oyp.norp
from a friend to a friend to us
Seb Np
10/30/99
(...)
Q. Why is a ghost such a messy eater?
A. Because he’s always a goblin.
 
Google Groups: alt.tv.buffy-v-slayer
Ghost Puns
Stan Kegel
8/23/00
(...)
Why is a ghost such a messy eater? Because he is always a goblin.
 
Google Groups: alt.humor.puns
Halloween Puns of the Weak 10/19/01
Stan Kegel
10/19/01
(...)
Why is a ghost such a messy eater?
Because he is always a goblin. (Joke of the Day)
   
Google Books
Fun Campfire Ghost Stories
By John Bradshaw
LuLu Press (Lulu.com)
2009
Pg. 113:
Why was the ghost such a messy eater?
Because he was always a goblin!
 
Google Books
The Funniest Spooky Joke Book Ever
By Joe King
Kondon: Andersen Press
2013
Pg. ?:
Why is a ghost such a messy eater?
Because he is always goblin