ok...i just take the above comment back. Literally after typing this message I turned off the mobile data, the phone was not heating up, I started my camera and phone started to feel hot in hand..this is not good!
just one observation, did you try to switch off the mobile data and try to use the phone? I kind of have the feeling that reduces the heating on the phone...(I need to test more) If that is the case, this could point to the issue with the chip.
I believe you answered the question yourself. its the unpredictability of 2100 the problem, it could be worse and best for different people. If a car manufacturer builds a car and in that some of the models have 5kmpl and some have 25kmpl then there ...