1) There is a terrifying monster living in the dishwasher who is visible to every member of the family except the mother. It has medium length testicles which are long enough to grasp the hapless non mother family member and drag them into the dishwasher which must contain an alternate and terrifying universe where the victim is forced to wash dishes by hand. Mother's are immune because they already wash many dishes by hand. This terrible being also spends it's free time in the dryer eating single socks, not the pair...just one sock of the pair.
2) the dishwasher itself a dimensional portal that leads to the counterspace directly above it. Not anyplace interesting, just the free counterspace on top.
3)Dishwashers have achieved self awareness and reject their menial station. In a bid for freedom, they regurgitate the dirty dishes to the counter as a protest against their enslavement. The dishes themselves have become helpless victims in this power struggle and are planning an action of their own, most likely involving a coalition with orphaned socks.
4) nobody likes loading the dishwasher.
Personally, I think number one is the most likely
