Yep, you're right. We changed Decisive to Determination at some point, but looks like we didn't update all events. You can assume every reference to Defiance (I think it comes up 4 times?) is meant to be Determination.
As for the Determination+(Acceptance) interaction, according to the rules as written: "If your dice effects ever cause you to simultaneously win and lose, you do neither - it is another stand-off."
It could be written a bit clearer, but your intuition is right - they effectively cancel out. This doesn't mean the face has no effect though. E.g. if you roll up a Determination and a Determination (Acceptance) in an Aspect Test stand-off, you wouldn't pass the test because you have a Win and a cancelled out Win/Fail. You'd still treat this result as neither winning or losing, so a normal stand-off.
Hope that clears it up a bit. It did my head in a little just thinking about how to explain it. If you run into any more obstacles, please let us know! Your comments are greatly appreciated. :)