Ruby struct marshal glitch

ruby_struct_marshal.rb

class WorkingExample
  def initialize
    @foo = 1
    @bar = 2
  end

  def marshal_dump
    @foo
  end

  def marshal_load(foo)
    @foo = foo
  end
end

class FaultyExample < Struct.new(:foo, :bar)
  def initialize
    super(1, 2)
    @qux = 3
  end

  def marshal_dump
    foo
  end

  def marshal_load(foo)
    @foo = foo
  end

  def inspect
    "@foo=#@foo,@bar=#@bar,@qux=#@qux"
  end
end

a = WorkingExample.new
puts "WorkingExample before dump and load: #{a.inspect}"
puts "WorkingExample dump #{Marshal.dump(a)}"
puts "WorkingExample after dump and load: #{Marshal.load(Marshal.dump(a)).inspect}"

puts

b = FaultyExample.new
puts "FaultyExample before dump and load: #{b.inspect}"
puts "FaultyExample dump #{Marshal.dump(b)}"
puts "FaultyExample after dump and load: #{Marshal.load(Marshal.dump(b)).inspect}"


=begin
WorkingExample before dump and load: #<WorkingExample:0x007fa18209ca88 @bar=2, @foo=1>
WorkingExample dumpU:WorkingExamplei
WorkingExample after dump and load: #<WorkingExample:0x007fa18209c830 @foo=1>

FaultyExample before dump and load: @foo=,@bar=,@qux=3
FaultyExample dumpIU:FaultyExamplei:    @quxi
FaultyExample after dump and load: @foo=1,@bar=,@qux=3
=end