Base Not Recognizing Open Sensor

Been having problems with the base not recognizing my back door sensor is open. This happens when the door has been open for long periods of time, if I close the door, open and then arm, it will recognize. I've called customer service twice now and their only advice is to move the sensors around, seems like bad advice to me, considering the base station notices the sensor opening and closing. Has anyone else had this same problem?

Not very good piece of mind, if I were to leave a lower level window open all day, forget I have it open, arm my alarm in home mode, someone could enter my home through the screen.