I got it last week... it's possible the battery that came with it has drained, but unlikely. The first part of the video is in one take (continuous). If I watch the sensor while being out of its range, the LED does not flash. It seems to only flash when it detects motion. I think that the sensor is detecting motion but sometimes is not communicating it to ISY. Another thing I've observed is that sometimes it will leave the light on - rather than turn it off after no motion for 30 seconds. When it does this (leaves the light on), later I can pass through and observe that the LED flashes when it sees me - 30 sec later it will turn it off.
I don't see any "misses" in the ISY Log. Every time the MSII tells ISY that its status is "on", the lights in that scene are set to "on". Every time that the MSII tells ISY that the MSII status is "off", the lights are set to "off".