Color change in duck meat!
I have seen the same phenomena with cooked hamburgers and steaks.  My research led me back to part of your question having to do with duck meat being characterized as red meat.

What differentiates red meat from white meat is the amount of myoglobin in the meat which absorbs oxygen from the air.  All red meat, when exposed to air, will turn bright red.  I have only observed this with raw or relatively rare cooked red meat so if your duck was not cooked beyond medium, that could be the answer.  Like you, however, I did not find any material that cited the exact scenario you described.

Here are my links to the articles on myoglobin in red meat:

http://scienceline.ucsb.edu/getkey.php?key=1859

http://m.wisegeek.com/what-is-the-difference-between-white-meat-and-dark-meat.htm