The Buzz Plothole

The creators actually said something in the lines of this, it is natural to them but they can also go against this with enough will. The toys should have quickly explained this though. Wouldn't be hard to put in the script.

Buzz: "I don't know why but a soon as one of those human creatures are nearby it just makes me totally freeze."
Woody: "Yeah, well, that is a reflex all of us toys have."

Solved.