The way I see it is that Buzz Lightyear is simply in denial and suffers from a form of an identity crisis.Throughout the film Toy Story Buzz claims to the other toys that he is not just a toy and he truly believes he is on a mission to stop the evil Zurg.Woody spends time trying to convince him otherwise,such as showing him his buttons and wings.Buzz denies this.However whenever Andy is around,all of the toys,including Buzz stop,moving and remain lifeless.The reason they do this is so humans do not think toys are alive,which brings me to my conclusion:Why would Buzz care if Andy thought he was real or not if he himself did not think he was a toy?He did not believe he was a toy, so why act like a toy?Maybe he wasnt acting that he was a toy, but maybe he was acting that he was on a space mission.Deep down,Buzz know he a toy, but struggles to accept the truth that he is not, nor will he ever be, what he dreams of. This is just my opinion,I make no claims of this being 100 percent factual