soft plastics molding?

hey guys, is this an issue y'all see often? i had a bag of powerbaits blue fleck worms for a while and just recently looked at them. i found they got molded. checked all my other baits but they seem fine. is this from some moisture in the bag or something? any good way to keep from happening?

See it all the time with powerbaits if they just sit for a while. I have lost several 100 count bags over the years, won't buy the big bags anymore because of it