New phenomenon: Double time jump at the end (SPOILERS)
Now that I think about it, the last jump depicted in the movie was actually a double-jump (or maybe a "jump-squared").
Sam and his sister were already in the past, as their younger selves in that warehouse. Then, already in the past, they both jumped farther back in time again to when they were kids in the fire.
I don't think this has been shown before in a "Butterfly Effect" movie: where a character, already in the past, can jump again farther back into the past, without returning to the "present" first.
Since this is established, then why couldn't the sister, trapped in the fire at the end after she had already jumped backward in time twice, just jump back in time once more to an hour earlier, and just walk out of the house before the fire started?