Its for sure the phone, and its not solved in later versions either (at least not the way I do see this error). Im currently running on 4.1.0.128 (latest), so nothing to flash.
My solution is to use the "sip proxy ip" and "sip backup proxy ip" instead of just pointing to a SRV record, as this way will make the phone try to re-subscribe all the way. While on SRV I have tested that its stops as soon as it gets an 408 or 503 SIP error message.