Single Experience Orb Not Collecting

This bug has been appearing for as long as I've been playing Minecraft, and it's never been mentioned or fixed. After gaining exp in Minecraft, you'll notice a single orb that hasn't been collected. You'll go up to it, and it will go toward you, but it won't be collected, nor will your exp bar go up. If you Save and Quit and reenter, the exp orb will be gone.