Since I've never seen one up close and personal, this may be completely off base, but is worth the suggestion. I've read that the keys on the keypad can leave impressions on the screen, this is probably not the problem since people are getting them over the palm rest.
My thought is maybe something related to heat from the battery and such could be a factor. This is just an uneducated guess.
Anyways, one thing I've read to eliminate the problem with the keypad impressions is to put a cloth (screen wipe, what have you) between the keys and the screen to protect the screen. If it is heat related or anything coming from the keypad side, this may protect it from happening in the future for anyone concerned.
Again, just a thought for prevention.