Ordinarily, when two item entities containing the same item are near each other, they will combine into a single entity. However, if one or both of the items has an Age of −32768, they will not combine.

Steps to reproduce:

1. Place and power a Repeating Command Block with the following command

   execute as @e[type=minecraft:item] run data modify entity @s Age set value -32768

1. Get a stack of 2 of any item from creative mode.
2. Press Q twice

Expected behavior: Items combine into a single entity, indicated by the presence of only a single shadow

Actual behavior: Items do not combine, indicated by the presence of two shadows.