House Trained Dog Started Pooping Inside?

I have a 12 month old Cockapoo who has been pretty well house trained for the past 6 months. He will cry at the door when he needs to go outside, and he is taken out shortly after eating. He has been having an increasing amount of pooping accidents in the house. Often times he will ask to go outside, pee and a few minutes later poo in the house. When he goes to the bathroom outside he is praised and given a treat. How do I stop him from going to the bathroom in the house? It's happened twice this week!