I picked up on it the first time I saw the movie in the theaters. I was surprised when so many others complained about the scene later.

Bruce wouldn't respond that way to "Martha" in just any other situation. You are oversimplifying the scene and the issue of his PTSD. It has everything to do with the fact that he was fighting Superman--someone who makes him feel like a weak little kid--at the time. This is the most trauma triggering stimulus there could be for someone in Bruce's situation.

Bruce is responding to Superman as he wishes he could have to his Mother's killer. Superman makes him feel powerless like he felt when he watched his parents die as a kid who couldn't do anything about it. (Conversations with Alfred in the bat cave set this up early in the movie). Bruce isn't going to be intimidated and let his metaphorical mother die in this situation.

As he takes down Superman, he is living it out like a ten year old blinded by powerless rage. It's why he doesn't see Lex's manipulation for what it is (the ultimate edition makes this clearer), and why he doesn't see Superman for what he really is. In the moment when he is about to kill Superman (and ultimately "save Martha" by taking out the he threat to mankind), it isn't just hearing the name "Martha" that is so disorienting (Bruce no doubt hears this name regularly without dropping everything). Clark says "you have to save Martha, you're letting him kill Martha". In Bruce's subconscious he was "saving Martha" by killing Clark. These contradicting statements at a time when he is at the height of rage and reactivity are what pull him out of it.

EVERYTHING Batman does is to symbolically "save Martha"--it always has. It's why he became a hero. So this moment is like Superman charging in the sun or Green Lantern charging his ring.

Bruce steps back pulling out of his blind rage, killing Superman is killing Martha? No I'm saving Martha? Why did you say that name? What is going on? He has a mother...this humanizes Clark. Bruce is reminded why he does what he does to save mother's not kill them. He saves kids. In that moment he shakes off his blindness and is a detective again--immediately seeing Lex's manipulations for what it was.

Hence his response, "I make you a promise, Martha won't die tonight."