The original UPC is for the first version of the disc, which was recalled due to not playing in numerous players, as well as a problem with the dynamic compression flag. The additional UPC sticker indicates that you have the corrected version of the disc.
Does this issue also relate to why there seems to be two different packaging versions. Based on pictures I've found on the internet there seems to be one version where the picture on the case is Robert Downey Jr. and not title and on the slip cover is the Iron Man suit with the Iron Man and "Ulitmate 2-Disc Edition." The other packaging appears to be cover art that was on the slip cover except it's directly on the case and there doesn't appear to be a slip cover. If I had to venture a guess it would be that with the original packaging included the Slip Cover. When it had to be recalled, instead of reprinting the the cover art for the sake of a new UPC they put a sticker on it as was mentioned. Then after the original packaging had be used up they decided that the new ones produce didn't need to include the slip cover. I bought it used and and the set sent to me didn't include a slip cover but i think it was suppose to because it has Robert Downey Jr. on the cover and not Iron man and my UPC matches the defective one. BTW I did test my disc in my PS3 and it seemed fine though I only watch the first minute of the movie