Alarm.com will show them in an activated status for an extended period after activity. This is normal. See the support thread below for info on how this works:
Sensor Activity Monitoring (SAM) is a feature for Alarm.com accounts. When Sensor Activity Monitoring is enabled, the specific status of sensors is shown on the website. For example, door/window contacts will show opened or closed, and motion detectors will report as active or idle. This feature does not affect reporting to monitoring stations.