Problem with wizards containing has_many :through relationships

If I have a Question model, for example, with a has_many :answers, :through => :question_answers relationship, and create a wizard with a step allowing a user to check the answers, the wizard retains the associated models when :persist_model is set to :per_page, but if :persist_model is set to :once, the associated answers are not retained.  Any way around this?
