I understand most of things that happened in BBS, except for one thing. When Braig talks to Xehanort, Xehanort says someone with light in their heart cannot take someone else's heart. So... what happened there? If Terra didn't take Aurora's heart, then who did? We clearly saw Terra doing it!

Terra took Aurora's heart. We know that for a fact he did. I'm not sure that you're totally understand the context in which it's being said..

Tecnacly it wasnt terra it was maleficent using terras body and what she did was control his mind by making the light in his heart disappear long enough to steal auroras heart.

Terra didn't take Aurora's heart. He just released it .-.

Terra took Aurora's heart. We know that for a fact he did.

But Master Xehanort said people like Terra don't have the power to steal hearts. Then Braig response with,"You mean, his not the one who stole her heart?"

Yes we do see Terra stealing it but MX is hinting to that it wasn't Terra, so yeah...

It might have been MX behind the scenes

Ok, I don't think you guys are understanding what it is that MX is saying. What he is trying to is that Terra without any kind of interferance is incapable of stealing another person's heart i.e. Aurora's. However, in Enchanted Dominion we see that he does, after and that is the key word, after Maleficent takes control of him. Therefore it was not Terra but Maleficent who technically stole Aurora's heart. that is even further stated in Ven's story when he asks, "Can you tell me why she's sleeping?"

The good fairies said, "Long ago, Maleficent cursed here, now she's stolen her heart!!!"

I assumed it was maleficent possessing Terra's body in a similar way of Hades possessing Zack's body. Zack does say something along these lines: " I am not doing this" so when Xehanort said it wasn't Terra I am pretty sure it was the same thing.

EDIT: and what AJTREY said.

acully terra released aurous and beacaus terra has darkenees in his heart mx said peopel with just light cannot take hearts