I too have been having random reboots, however, the only difference to my issue over others I have seen is mine is a TOTAL shutdown. I cannot power the phone back on unless I pull the cover and remove the battery. I noticed the potential fix about cushioning the battery to provide a more secure fit. At times, when using my BT Headset (Moto Rokr S9-HD) when I set the phone down on its back, it will drop the call and the phone is off. At this time I notice the battery and cover are warm and that the battery rattled. (Shake your phone holding from the sides and see if there isn't a noise, now pinch the battery cover, thumb on screen, fingers on back and see if rattle goes away) So, I see the potential of TWO problems. My solution, and I will spend the next week checking this and repost my results....
I have used a piece of foil tape used by HVAC guys to seal duct work to wrap my battery ONLY on the sides and back of the battery where it contacts the battery cover. I didn't wrap the front (Phone side of battery) for conductivity and possible short-circuits, that otherwise might damage my phone. I decided on foil tape for TWO reasons, One, and primarily, this will act as a thermal sync to help dissipate heat, just as we do when building High-end PC's to prevent overheating the processors during gaming, and two as a "shim" to provide a tighter fit and prevent battery movement and possible loss of contact with the terminals. If this seems to solve the problem, I may post a YouTube video of the fix. Hoping this works. Mine is so infrequent, that it may be difficult at best to verify until others in the community try it out themselves.
M