Currently the ItemStack class has overriden the Object#hashCode function. I am requesting that this either be removed and use Java's default hashCode function or have the final modifier taken off so it can be overriden by plugins implementing the API. It makes sense for this to be so; a stack of dirt shouldn't be 'equal' to a separate stack of dirt with the same properties (material, count, data) because they will still always have a different location.