I some times have this issue, but it's down to a reflection from a window either on the sensor or mote.
I just close the blind that is causing the problem and it solves it.
I also have 3 motes 1 I got with it, 1 bought from a local shop and 1 I bought on ebay from china, this one is very sensitive and I don't use it much because it always flickers and adjusting the sensitivity of it thoughs off the others.
It would be great if you could adjust the sensitivity for each mote, but you cannot. So I have to live with it.
Try another mote if you have one, adjust your sensitivity and make sure there is nothing interfering with the sensor bar or inferred mote