fill-paragraph / fill region in latex (auctex) buffer

[David Reitter]

When I do fill-paragraph on a long line that starts with a %, the  
line is correctly wrapped and a % is added in front of each line.
This is in latex-mode (AUCTeX).

fill-paragraph-function is nil.

When I select a region with the same text, the behavior is different  
- no %'s are inserted, and I get an undesirable result.
This is annoying, because I would want to use fill-region on a whole  
buffer in order to wrap lines, and it turns all the commented out  
stuff into text that appears in my latex document...

Is this a bug?
If so, is it due to Emacs or to AUCTeX?