Container form elements are missing proper form error classes

The container form element like fieldset or datetime-wrapper in the system module are missing the form error classes(form-item--error-message). They print the errors in simple div. One has to use the Classy theme or override the templates in custom theme to get the proper classes.
For example the form-element template has the proper form-item--error css class. This looks like a bug since those error classes are in the core and therefore the Classy template should not be required(it does not add anything else).