Turns out the itemid can change on world load.

Use the unlocalised name instead as this should be constant. Anyone using the stack size in the unlocalized name method should be shot.

src/main/java/mekanism/api/util/StackUtils.java

@@ -242,6 +242,6 @@ public final class StackUtils
 
 	public static int hashItemStack(ItemStack stack)
 	{
-		return Item.getIdFromItem(stack.getItem()) << 8 | stack.getItemDamage();
+		return stack.getItem().getUnlocalizedName(stack).hashCode() << 8 | stack.getItemDamage();
 	}
 }