When in creative mode, speed dropping (holding Q) a stack of anything from the hotbar/survival inventory (in creative) looses about 45-60 items total.
(As in, dropping a stack (64) items makes 45-60 items disappear mid air, resulting in the stack picked up only having 4-14 items total.)
From a little testing, this only seems to happen in the creative inventory, not in survival or in a chest/ender chest