I have not seen this problem before. But if this problem is reproducible, it's very easy to troubleshoot.
We need detailed "Cisco CallManager" traces and a packet capture from the phone.
If the phone "reset by itself", there could be two reasons (besides hardware problem):
1) CUCM sent it a "reset" instruction
or
2) It lost keepalives from CUCM.
Michael
http://htluo.blogspot.com