Being a patent attorney, I was very interested in how much truth there was to it. So I did some research on this story.

It turns out that
a) the Duck story would have been novelty-destroying prior art: given the story, any Patent Office would have rejected Kr?yer's patent application.
b) there's no evidence that the Duck story has *actually* been used to refuse a patent application.

All this and more details on my website at
http://www.iusmentis.com/patents/priorart/donaldduck/

Arnoud Engelfriet