The bug

When you for example have an inventory nearly full with any stackable item, and then pick up that item, you of course are only able to pick up a part of that stack, however, the rest of the items that you didn’t pick up then get dropped. This may cause you to accidentally drop items into lava, cactus or the void and destroy them.

Steps to Reproduce

1. Drop one stack of any stackable item (for example diamond blocks) on the ground, but don’t pick them up
2. Make your inventory completely full with that stackable item, that you used
3. Remove half a stack of that item from your inventory
4. Go into survival mode
5. Pickup the item

Observed Behavior
32 of the items were picked up.
But the other 32 items where dropped.
Expected result:
You should pick up 32 items and the other 32 items should stay on the ground and shouldn’t be dropped by the player.