Can you put up some pictures please? "Of the burnt stuff, and the rest of your affected fairings". I dont know if it is possible now, but you should see some part numbers on these fairing parts. This is something I hadn't ever considered to check for on any of my bikes, so I'm not sure. You probably have OEM fairings, just maybe you can find the part numbers and check from there. A raised stamp or, a painted stamp.
To catch on fire is a strange thing to say the least. It is safe to say, that shouldn't happen.
Unless, you somehow put the fairings on in a fashion that is not correctly positioned, "I dont think so, because its actualy kind of hard to do", you would notice this for one thing, because, then likely something just wouldn't look quite right. The headers are quite well thought out, and usually pose no problems with OEM parts. Any company making after market pipes does a pretty good job at making sure their parts work without burning up a customers bike. They want repeat customers, and word to get around that their stuff works great. Money you know, it does wierd things to people.
With all this written, I would say that the insulation was different, or a replacement piece.