Yes,you were right,the nymph had an injury to the exoskeleton
before the molt the chitin looked kinda healed and not white
http://img205.imageshack.us/img205/8091/snv31023jl9.jpg
but after the molt the damaged chitin fell off
http://img244.imageshack.us/img244/9884/snv31036lm3.jpg
http://img246.imageshack.us/my.php?image=snv31033wg2.jpg