Rails 3.1 _ids Bug When adding an association using `_ids = [association_ids]` for a has_many through relationship, ActiveRecord throws a RecordInvalid error if one of the association_id records does not validate. When used with a nested form, the update action will not render the edit action when `object.update_attributes` fails. Setup: 1. Install the bundled gems and rake the database 2. Run `Classroom.setup_data` in the console to add the default data Reproduce In Console: 1. Run `Classroom.add_invalid_teacher_to_classroom` Reproduce In Browser: 1. Navigate to `/classrooms/1/edit` 2. Check the Teachers box for ` Teacher ids 2` 3. Click `Update Classroom` Simple Form is used as a convenience to create the check box fields.