Can anyone explain why this happens?

mybox:$ ruby script/console
Loading development environment (Rails 2.3.5)
>> foo = Foo.new
=> #<Foo id: nil, customer_id: nil, created_at: nil, updated_at: nil>
>> bar = Bar.new
=> #<Bar id: nil, bundle_id: nil, alias: nil, real: nil, active: true, list_type: 0, body_record_active: false, created_at: nil, updated_at: nil>
>> bar.save
=> false
>> bar.errors.each_full { |msg| puts msg }
Real can't be blank
Real You must supply a valid email
=> ["Real can't be blank", "Real You must supply a valid email"]

So far that is perfect, that is what i want the error message to read. Now for more:

>> foo.bars << bar
=> [#<Bar id: nil, bundle_id: nil, alias: nil, real: nil, active: true, list_type: 0, body_record_active: false, created_at: nil, updated_at: nil>]
>> foo.save
=> false
>> foo.errors.to_xml
=> "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<errors>\n  <error>Bars is invalid</error>\n</errors>\n"

That is what I can't figure out. Why am I getting Bars is invalid versus the error messages displayed above, ["Real can't be blank", "Real you must supply a valid email"] etc.

My controller simply has a respond_to method with the following in it:

 format.xml  { render :xml => @foo.errors, :status => :unprocessable_entity }

How do I have this output the real error messages so the user has some insight into what they did wrong?