I have the same problem - the phone restarts. But I can stop the restarts by:
1) Turn of Bluetooth. When Bluetooth is on, it restarts 1-2 times a day. When using bluetooth for external devices it restarts more often.
2) Turn off wi-fi. And just using 3G/4G/LTE. When entering a 'known' wi-fi (home or Work) it surely restarts every time.
It's not a solution, but hopefully it's solved in 4.3 and 4.4. I have tried to reset phone, new simcard etc.