Defect Detector CSX Capital Sub Near Laurel MD MARC Station

Description

3/31/08: I didn't realize there was a defect detector south of where I was watching trains on the CSX while I was in MD, and I remembered Hickler90's video, so I caught the end of the detector calling out after the SB MARC from the previous video passed over it. Just after I left the station, I heard a NB MARC get caught by the detector. Would this train have to stop immediately? What could be causing the problem?