Dishwasher Overflows but Fill Valve, Float Switch, and Draining All Work!

I have a Frigidaire FDB520RHS2 dishwasher and it is now overflowing with water despite the following:

* My fill valve works flawlessly.
* The float switch also works perfectly; I have tested it 5-6 times in disbelief.
* It only overflows an hour to an hour and a half into the cycle (which is 2 hours).
* There is no soap or rinse aid involved with my testing.
* The draining works every time; any time I cancel the cycle, it drains for 90 seconds and never fails.
* I took apart the spray arm and everything else under it inside and cleaned thoroughly.
* I have the drain hose in a bucket on my workbench about 18" off the floor.

If the fill valve and float switch are working, what else could be causing it?

 

OMG, I just discovered that it's sucking water out from the bucket the drain hose is in!!

I'm going to consider this solved, but I'm still curious as to why this could happen, especially since I made sure the bucket was well above the highest point of the tub inside.

 

I'm guessing you're just using the bucket for testing ?

If the bucket is higher than the tub....... and the hose is full of water.....as soon as the pump stops, water drains back into the tub creating a suction on end of hose drawing water back in.

The siphon effect.

 

Yes, the bucket is for testing. I figured that the discharge pump was always spinning as the wash pump is spinning, making it impossible for this to happen. I guess I was wrong. Thanks.