Did the line unwrap from the self-tailer, or did the switch/relay contact get stuck closed? Either way, I don't even want to think about the possible consequences.

When I hired a rigger to go up the mast in Plymouth Rock a few years ago, they used my electric winch to haul one guy up while the other operated the winch -- but the rigger asked me to stand by at the circuit isolator switch so I could cut it off "just in case".