Standing on top of a dropped item stack, then dropping an item from the inventory, causes the stack on the ground to be picked up, but the items vanish.

Steps to reproduce

• In survival, get an item and drop it on the ground, for example ladders.
• fill your inventory with something that is not the same as the dropped item. (/give @p stone 50000 for example)
• Stand over the dropped ladder item
• Drop your held slot of stone so you can pickup the ladder item. Notice the dropped ladder item entity despawns, but the ladder items aren't in your inventory and your hand remains empty after dropping the stone items.