I use a Polar H10 heart rate monitor during my runs and when I end the run my heart rate monitor disconnects and it returns back to using the optical monitor of the watch. When this happens my heart rate which may be anywhere from 120-150 based on my polar but when it is disconnected, my watch will display "--" then something around 60-70 bpm. If I reconnect my polar it will go back to above a hundred but it takes my 945 a while before it displays a somewhat accurate value using the wrist based method. I am using the most recent public release, but this has been going on for a while even in previous updates.