While working on a furnace array for a server, I discovered an issue where the item loader I was using (which used hopper minecarts to pick items up off of a weighted pressure plate) seemed to only be picking up a percentage of the items I was putting into the system. As an example, I would load 25 stacks of smeltable items into the item input (5 minecarts with 25 stacks across them), but only three minecarts would be dispatched with 12 stacks of items across them. 

Examining the issue further, I discovered that using Ctrl-Q (or equivalent) to drop multiple stacks of the same item onto the ground within a certain time frame would cause some of those stacks to be deleted. Quickly dropping items onto the ground would result in greater losses, while spacing the drops out would result in fewer losses. 

This behavior does not appear to manifest when breaking a container with multiple stacks in it, such as a chest. Filling a chest with 27 stacks of items consistently results in 27 stacks of items on the ground.

A video demonstrating this bug is linked here: https://youtu.be/cI7ocLsneLc