In the PBS "American Masters" doc on Bing Crosby - coming in December -  
there is discussion of the Crosby/David Bowie duet of Little Drummer Boy by 
both  the director and head writer for the Crosby Christmas Special where it 
occurred.  Bowie showed up (because his parents loved Crosby) and was told 
they would sing  LDB as a duet. Bowie refused as he hated that song and felt 
it was too  religious. The writers quickly re-wrote the number so that it is 
Bing singing  LDB and Bowie is singing a different song at the same time.
 
More on the Crosby documentary later.
 
Steve Ramm