The 6 inches and then locked means there is power to the brakes. It's easy to differentiate between the brake controller and the breakaway switch.
The emergency breakaway will still function with the trailer umbilical disconnected from the tow vehicle. If you disconnect the umbilical and the brakes are still locked then your emergency breakaway OR your trailer wiring is the culprit. Try disconnecting all the battery negative cables and see if the brakes unlock.
If however the brakes do not lock when you unplug the umbilical cord then your brake controller or tow vehicle wiring is at fault.