I just received a super hot delivery of soup in a polypropylene container (the plastic symbol on the bottom is a 5). I noticed the lid was very pliable in comparison to the rest of the container to the point I could easily bend it and cause the surface to warp by poking it with my finger. After lifting my finger it would bounce back somewhat, but retain some of that warping. As it cools it's returning to it's original shape and becoming harder to manipulate.
I'm wondering if this implies melting/leeching has occurred and if I should just return the soup to be safe.