I don't know what the reason is but last year mine did the same thing. You can see in the picture there is a leaf (TOP LEFT) above with nothing and there was another one but it fell off. I don't know why, I'm sorry but I just wanted to ease your mind and let you know mine did that too...maybe we are both "not normal" but I figured the chances were good if mine did it too that this is a normal process.
Jen
