I played a little bit with the conveyor and the sensor form the starter tutorial. I noticed that if a MU is occupying the sensor and then I delete the MU either manually or with a think, the sensor continues to be occupied. In order for the sensor to be free, I first need to move the MU out of the sensor collision box and then I can delete it. In my opinion the senor shouldn't remain occupied if the MU that occupies the sensor is deleted.
Customer support service by UserEcho