1. Place an item into the first slot of a chest
2. Run /data modify block <pos> Items[0].count set value 99
3. Observe that when you run /data get block <pos> Items[0].count it states that it is 99, but when you open the chest it only shows as 1
4. Run /item replace entity @s weapon.mainhand from block <pos> container.0
5. Observe that the item count is correctly displayed while the item is in your inventory, or in your cursor.