Has_many: autosave => true skips checking when saving children

In both Rails 2 and Rails 3, if: autosave => true a has_many association, the assembly is looped and saved (: validate => false) is called in each child association. Why is this? We need a before_validation callback to execute for this child, but since then it will not save a value that passes validation.

What a good way? And what is the purpose of passing validation?

Any help would be greatly appreciated! Thank!