The two Sams got in to an argument about which one is a clone and which is not:
SAM2: You're a fucking clone. You don't have shit. SAM1: Hey, I'm going home. SAM2: You're not going anywhere. You know, you've been up here too long, man. You've lost your marbles. What, do you think Tess is back home, waiting for you on the sofa in lingerie? What about the original Sam? Huh? SAM1: I'm the original Sam! I'm Sam fucking Bell! Gerty, am I a clone? GERTY: Are you hungry?
Gerty would not answer the question.
Later Sam 1. has asked about his video messages that he sent to his wife while network communication was down:
SAM: Gerty... Am I really a clone? GERTY: When you first arrived at Sarang, there was a small crash. You woke up in the Infirmary. You suffered minor brain damage and memory loss. I kept you under observation and ran some tests. SAM: I remember, yeah. I remember that. GERTY: Sam, there was no crash. You were being awakened. It is standard procedure for all new clones to be given tests to establish mental stability and general physical health.
Why did Gerty suddenly reveal the secret that he was supposed to keep. In all other parts of the movie, he followed his programming - helped Sam in any way he could while keeping the secret for himself. Why did he suddenly change?