Your washer is siphoning, here's a video that explains it:
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https://www.youtube.com/watch?v=hpfcIuLLIYQ
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Your washer is siphoning,
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The purpose of a dishwasher air gap or anti-siphon is to prevent the siphoning and back flow of water. The water can flow back into the dishwasher which will leave water in the bottom of the dishwasher. The air gap or anti siphon prevents siphoning if sinks are drained simultaneously.