“He broke into song because he couldn’t find the key”

Do people really “break into song”? A musical one-line saying is:
 
“He often broke into song because he couldn’t find the key.”
 
The pun-filled saying has been cited in print since at least 2002, when it went viral in lists with other puns.
 
 
24 December 1964, Pittsburgh (PA) Press, “Dear Brings Rain, Dear,” pg. 1, col. 2:
Press Weatherbird Donald Dingbat couldn’t find the key so he broke into song to wish all his fans a Merry Christmas and a Happy New Year.
       
Google Groups: alt.humor.puns
Puns of the Weak 03/15/02
Stan Kegel
3/16/02
(...)
He often broke into song because he couldn’t find the key. (Jerry Ulett)
 
Google Groups: alt.humor.puns
Puns of the Weak 03/29/02
Stan Kegel
3/30/02
(...)
He often broke into song because he couldn’t find the key. (Jerry Ulett)
 
Google Groups: alt.fifty-plus.friends
To pun is human
Yoj
4/9/02
(...)
16. He often broke into song because he couldn’t find the key
 
13 April 2002, The Post and Courier (Charleston, SC), “Keep on; the punny side of life” by Elsa McDowell, pg. 1:
- He broke into song because he couldn’t find the key.
 
Google Groups: alt.humor
“Puns of the Weak” 05/24/02
Stan Kegel
5/24/02
(...)
He often broke into song because he couldn’t find the key.  (Marina)
 
Google Books
The Songwriter’s Hook Book
By Jon Batson
Instantpublisher.com
2003
Pg. 81:
He often broke into song because he couldn’t find the key.
Groucho Marx
 
Google Books
E-Mail Humor
By Louis G. Morton
Victoria, BC: Trafford Publishing
2005
Pg. 6:
He often broke into song, because he couldn’t find the key
   
Twitter
Dave Ingram
‏@dmi
Musical thought of the day: “He broke into song because he couldn’t find the key.”
6:30 AM - 12 May 2008
 
Google Books
Hilarious Jokes You Can Tell Anywhere
By Silvio Famularo
Durham, CT: Strategic Book Group
2011
Pg. 142:
He often broke into song because he couldn’t find the key.
 
Google Books
Dr. O.K.‘s Wit, Wisdom and Whatever
By Otis LoVette
New York, NY: Page Publishing, Inc.
2016
Pg. ?:
He often broke into song because he couldn’t find the key.