When I try to open by drag and drop the attached file, Emacs keep asking
me 'Try to auto fix whitespace loss? (y/n)'. No matter y or n, the
dialogue will appear again and again until I kill the buffer.

I enable whitespace mode using (add-hook 'diff-mode-hook
'whitespace-mode).

GNU Emacs 23.0.92.1 (i386-apple-darwin9.6.0, NS apple-appkit-949.43) of
2009-04-15 on 64-71-7-214.static.wiline.com