Seat belt reminder icon

I have a 2014 Prius V seven seater. A few times while driving, the rear passenger seat belt reminder display on the dash lights up even though the passengers are belted in securely and stays on until I stop the car and then power off and on again.
Has anyone experienced this ?

 

Thanks for your responses. At startup the seat belt reminder icon shows a red dot for each of all the 5 rear seats if the seat belts are not latched. If the passengers (doesn't matter if they are big or small) are seated and their seat belts have been latched, the dot turns off for the corresponding seat. Only the red dots for the unlatched and unoccupied seats remain. After a few seconds the whole icon turns off, regardless of whether the seat belts are latched or not. This is normal operation.

However the experience I wrote about is when the icon with all the five dots suddenly turns on while I am driving and remains on for the rest of the journey. There are no other indicators showing that a door is open and the road is not bumpy. I asked one of the passengers to unlatch their belt and then latch it again to see if that would extinguish the icon but it remains on. This has happened a couple of times so far. During one of those times when the icon was still on, I stopped at the next traffic lights when traffic was stopped and powered the car off then on again and the icon turned off and remained off for the remainder of the journey.

I've also checked the operation when the icon has turned off and a passenger then unlatches the belt - the seat belt reminder icon turns on and the red dot corresponding to that seat appears. It turns off when the belt is then latched.