Maybe he isn't finished going when he comes in the house? Try waiting a few moments after he's gone, and then bring him in. I am training Bear to go outside now, and I've noticed sometimes he squats in two or three different places... if I don't let him finish (ie, I am in a hurry for work, see him squat, and rush him in right after), then he comes inside peeing the whole way... he also does this on his pee pad. Sometimes if he is excited to get a treat or eat breakfast, he will walk off it, still peeing!!!
He just hadn't finished yet.
-O