Well I don’t think the OP got the proper answer to this so I might as well resurrect the thread. I’am pretty sure his device wasn’t overheating while in idle, but rather when running CPU/GPU intensive apps, or background tasks for that matter.
Would say its not normal. Can also depend on app you run in background. i did try OSMAND and this app heats the MX3 up due a lot loading of the different layers of the map it uses.
Other than that mine is fine.
When you flash new firmware be sure u set clear data.
OSMAND? navigation app? Try some hw demanding game like beach buggy racing and report back.
Personally I can confirm that when fully using the hardware, the battery can get up to 50+C (!). Kinda limiting factor if you are after raw performance and want to fully utilize your hardware. :)
So if battery gets to 48C, the background apps might be the cause, but I see nothing to suggest that the phone is faulty given the fact that at full load it can get even hotter than that. You can fry eggs on that thing.