Wow--the first actual photograph I've seen of "delamination"!! I started using Thermarest pads around 1981 and over the years have had many of them and basically lived on them, whether in tents or bedroll camps or up at the Tipi where I used a series of Camps Rests(now called the Base Camp).
In all those years I had about 3-4 pads delaminate and produce an air bubble as shown in your post. The outside fabric pulls away from the inner foam core, or whatever is used to keep it attached, making sleeping on it nearly impossible. I spent many nights hunched over a big air bubble trying to sleep--details(and cursings)are not forthcoming.
I emailed Thermy about it 2 years ago and they told me it's due to long "overuse" and "body oils". A year before that I took in a bladdered Camp Rest to Footsloggers, an outdoor store in Boone, NC. The clerk asked me, "Do you use this pad all the time?", as if constant use somehow negates the warranty. I stood my ground and demanded a replacement, fed up with all the delaminated Thermarests I have owned. He finally called Cascade Designs and they told him to give me a brand new Camp Rest, as the bladder was a manufacturing defect. He did so reluctantly. Hooray. So I got a new pad.