http://www.cbsnews.com/8301-504763_162-57516710-10391704/colorado-man-wayne-watson-wins-$7-million-in-popcorn-lung-lawsuit/
It is reported that major manufacturers of popcorn stopped using diacetyl and are using 2,3-pentanedione which is also found to be a respiratory hazard.
The symptoms of popcorn lung disease include, scarring and hardening of lung tissue, dry cought, shortness of breath, night sweats, fever, skin peeling.
Information on flavor related lung disease can be found from NIOSH website here. http://www.cdc.gov/niosh/topics/flavorings/