I cannot find info on this specific washer so the following is just for washers in general.
The fill level is controlled by a pressure switch. There is a hose that runs to the bottom of the tub. As the washer fills, this hose also fills with water, air pressure builds up in the hose and when it equals the level switch's set point it stops the water and starts the agitate. It is in the control console.
Possible causes are
1. The water level switch itself
2. An air leak in the pressure tube.
3. Some crud at the bottom of the hose which is stopping/slowing the water from entering the hose.
4. Hose is not positioned correctly in the tub.
In your case the last three would be at the top of the list with #4 at the top of the list.
I am not sure how the hose attaches to the tub. On some units it attaches to a fitting on the outside of the tub, on others it just goes between the inner and outer tub.
Check that it is properly positioned. If it is not positioned correctly the tub will fill with a certain amount of water before the hose starts to fill this will give an overfill condition.
For crud just remove the hose from the switch assembly and blow into it.
Check the hose for hairline cracks or holes. Also cut half an inch off the hose and re-seat it to the switch assy, just in case there is an air leak at the switch. If brittle or cracked replace the hose.
Here is a good link with gerneral washer info.
http://www.applianceaid.com/washers.htmlHope the above makes sense!!