This has tripped people up more than once. Doors are two-component items. ACACIA_DOOR represents the top-part of the door, while ACACIA_DOOR_ITEM represents the bottom-part and also the item id. Use ACACIA_DOOR_ITEM when creating an ItemStack.
Tip: If you are unsure about an item id, launch Minecraft in creative mode and enable Advanced Tooltips by pressing F3+H. The real item id will be displayed in the tool tip as you hover over items in the creative inventory. For example, hovering over an Acacia Door would display
Acacia Door (#0430)
Use this information to lookup the appropriate Material enum in org.bukkit.Material, which in this case would be ACACIA_DOOR_ITEM.
solved Strange behavior of ItemStack