module Foo
  def create_methods(*args)
    args.each do |fieldname|
      fieldname = fieldname.to_s

      define_method fieldname + '_field' do
        @fields ||= {}
        begin
          raise 'foo'
        rescue
          puts "#{fieldname}_field (#{$!.backtrace[0]})"
        end
        @fields[fieldname]
      end

      define_method fieldname + '_field=' do |value|
        puts "#{fieldname}_field = #{value.inspect}"
        @fields ||= {}
        @fields[fieldname] = value
      end

      define_method 'writeback' do
        @fields.keys.each do |fieldname|
          puts "#{fieldname} = #{@fields[fieldname].inspect}"
        end
      end
    end
  end
end

class BaseClass
end

BaseClass.class_eval do
  extend Foo
end

class FooClass < BaseClass
  create_methods :bar, :baz
end

b = FooClass.new
b.bar_field
b.baz_field
b.bar_field = 'barr'
b.baz_field = 'bazz'
b.writeback
b.bar_field

# The error manifests itself here: variable fieldname has the value 'bar'
# where it should be 'baz'
b.baz_field