Whats the difference between a fake an real keyblade?
They both can release hearts and own you right?
And i like associating roxas saying "shut up" to when ven says it to braig heh.
I think this theory explains it rather nicely.
Originally, I took issue with the claim that Xion's keyblade was "fake." We know that she sends hearts to Kingdom Hearts. So if you have a fake keyblade that looks like a real keyblade, hell, probably tastes like a real keyblade, but most importantly
acts like a real keyblade, then how is it fake? It really isn't, the label "fake" is nominal at best. Artificial, maybe, but if I made an artificial giraffe from scratch and it looked/acted/etc exactly like any giraffe born of natural means, then how is that FAKE? More disconcerting is the fact that, by giving a fake keyblade the abilitiy to release hearts, it robs the real keyblades of what makes them special.
But this provides an answer.
Basically, up until Roxas inadverdently performs the rite on Xion, her keyblade was fake. And it wasn't actually sending hearts to Kingdom Hearts, just doing what any other normal weapon would do. In other words, it only looked like a keyblade (similar to how Zexion had a keyblade when posing as Sora, it was based on the projection of memories). But after that, with her own, real keyblade, she was truly releasing hearts.