Check for: A siphoning situation. You need to have an air break in the drain hose where it enters the stand pipe. Also look for a clog or restriction in the air tube or air dome where the water pressure (water level) switch attaches to the tub. Next thing to check is the integrity of the pressure switch itself. Although rare, it can fail electrically.

If the water continues to fill after you unplug the machine, the truble is in the valve itself: It should be replaced.

Check the action in all the different wash cycles to rule out the timer.