Xiaoming,
I have not been able to solve the problem yet - it has a very low rate of occurrence. I have not observed it since updating to iOS 6.1.0, and it was reported on the apple bluetooth-dev mail list that it may have been fixed then. Your account of the issue on iOS 6.1 gives me less confidence in that though!
Aslak,
I use a characteristic to wait for the iPhone to finish service discovery before requesting the connection parameter update from the peripheral. This method seems to work well and mitigates the issue with connection drop from connection parameter update during service discovery.
LPRF Rocks The World,
I don't think this one is related to the channel map update, my sniffer captures never show it getting to the point where a channel map update would occur. It is good to know that a chan map update issue exists though! Here is the line that causes the disconnect from my sniffer capture (the connInstant for the updated parameters to take affect is highlighted in red, the current event counter is highlighted in yellow - you can clearly see that the connInstant is in the past):
Frame,Access Address,Event Counter,Side,Control Pkt,connInstant,length,delta,timestamp
685 0x50655320 0x0076 1 LL_CONNECTION_UPDATE_REQ 0x0071 27 00:00:03.509752 2/22/2013 12:31:08.207936 PM
-Tyler