DS has this habit of behaving great until we comment on it, then going nuts. Today, for example. He was awesome this morning. He played with DD, picked up messes, made his own lunch, etc. Then DH came downstairs and I commented to him how great DS has been and told DS that if he kept it up, I'd let him use my lunch bag and take his lunch to school on Tuesday (it's a big deal for him). The second I said that, he went crazy. He started getting into things he wasn't supposed to, lying to us, arguing, whining, etc. The day's been crazy ever since.
DH and I have both noticed this. The second we say something nice or tell DS we're about to go somewhere nice because he's behaved well, he starts acting up. We've had to cancel outings more than once because DS wouldn't get dressed, refused to eat lunch, whatever. But if we don't comment on his behavior or mention an outing, he usually acts nice the whole day. Which means that we usually don't get to go places because the second he finds out we're going he starts acting up.
What is up with this? Isn't positive reinforcement supposed to be a GOOD thing? Why does DS start acting like a brat the second we say something nice to him?