Happens to me all the time. I think that there is still some soil or whatever made the stain still in the carpet backing or pad and when you suck up the water, it pulls it up. So, even though you cleaned the carpet "on top" when the water came back up, it was dirty again. At least that is what happens here. After I clean it there is still dirt at the bottom when you spread the threads. At least you know it is cleaner than it was! lol