Ruby 1.8/1.9 change regarding super inside a proc

gistfile1.rb

class Human
  def self.speak what
    what
  end
end

class Pirate < Human
  def self.speak what
    proc { super }.call
  end
end

# RUBY_VERSION "1.8.7"
Pirate.speak('Hi!')  # wrong number of arguments (0 for 1) (ArgumentError)

# RUBY_VERSION "2.0.0"
Pirate.speak('Hi!')  # nil