I will tell you all the exact details of what happened:
I was on route 15, to the north where you go up a waterfall. I opened the bag and selected the key items pocket. I used the circle pad to scroll down, and I saw the bicycle hilighted in yellow. One space below that, where the mega ring should have been, it said bicycle again. I selected it, and the yellow went away. I scrolled down and up again, and it turned into the mega ring!
What happened here?