This problem happens regardless of quality setting, even at 100% in PDN it still causes this issue. It's due to Chroma Subsampling. Photoshot and Irfanview allow this to be disabled, PDN doesn't, I'd like the option to disable it.
More info
http://www.albumartexchange.com/forums/viewtopic.php?f=2&t=1811
http://www.impulseadventure.com/photo/chroma-subsampling.html