New Crack in Case After Phone Ran Hot

Just a few days ago I took my phone out of my pocket and realized it was extremely warm. I woke it up to use it and immediately got the message that the battery was almost dead. It had a full charge from a couple of hours before and I had only used it for a few minutes since. I figured some background process was running wild so I did a total reboot then turned the phone off since the battery was almost gone anyway. When I got home I charged it up again and haven't had a problem with it. However for the first time I saw a definite crack in the plastic casing at the headphone jack as well as some stress lines in the plastic around that area. From earlier threads about cracking cases I was familiar with what other people had seen on their phones and realized mine was just like those.

My belief is that when the phone heated up it caused the plastic to flex and crack at its thinnest area. I have the black phone and the crack is very hard to see although if you run a fingernail across the area you definitely feel change in the surface. I'm not taking it in to an Apple store yet because it's so difficult to see and this phone was a replacement for another that had developed a visible flaw under the front screen. However if the crack becomes more prominent or if others develop I will take it in. I'm just wondering if the cracks that others had seen in prior threads were also related to the phone running hot for some reason.
John