Switching from an item with a right-click function to an enderpearl causes the enderpearl to disappear in creative mode. This only happens if you hold the right-click button the entire time, not letting go to switch items. If the enderpearl is in your offhand spot, it disappears until you press "f", but if the enderpearl is in your hotbar, it will disappear until switched into your off-hand.