Went to a house to change two hallway fixtures that the home owner has been having trouble with. Pulled first one down the wires were melted together and burn spots on the drywall. Saw an added wire with just the neutral wire connected in box. ( hot wire was not connected to anything.) Traced wire to an added ceiling fan in a bedroom they pulled a Romex to the switch in the room (which was originally controlling a receptacle) to get the hot. Got everything rewired and all is good but am not sure why the breaker didn't trip due to the short in the light fixture?