BAH! You still misunderstand... imagine Battlefield, pretend it has a completely flat bottom (will make it easier to explain). So Ike is on the left of the stage, maybe he's about to grab the edge but instead his does the Up-B. His sword goes flying up, and has now moved
just a little to the right so it is above the main platform (could be significantly above, but whatever) Ike has still fallen for a total of like a quarter of a second, and Ike's position now is
just to the right and below Battlefield's main platform. Now, Ike is programmed to leap for the sword (which is above the main platform) and hits the main platform in the middle of his leap since he's under it. Does he go right through the main platform so he can retrieve his sword?
I doubt it, but I'm just saying it's a little hard to imagine what will happen exactly. My guess is that when Ike hits the main platform (under it) he falls to his death without the ability of doing anything but move slighty right and left (sort of like most characters falling after using their Up-B) and his sword simply disappears the moment he's supposed to be grabbing it, or the moment he dies, or the moment he re-enters.
That's the best I can explain it without pictures....lol