It says "clean," but they're still dirty

I was making lunch this afternoon, and discovered that I needed clean plates for the kids. Little light on the dishwasher proclaimed that the contents contained within were clean! So why is it, then, that the dishes I needed were still dirty? I had run the dishwasher, with soap. The cycle was complete, and in fact, the other dishes were clean. So how is it that all the utensils, all the cups, bowls and serving dishes were clean, yet the children's plates were still dirty? Am I the victim of some weird phenomenon of physics?

Apparently not. You see, the top of plate 1 was clean. And the bottom of plate 12 was clean. (Yes, we have 4 children and they like to eat three times per day. Ridiculous, isn't it?) This is what happens to me when I try to do, I don't know, say 18 things at once. I forget that I stacked the plates in the dishwasher so I wouldn't leave a mess on the counter. I think today's load will contain about 16 or 20 plates...just so I can catch up, you know.