Non-existing form_id can be retrieved, prepared, processed, and even executed

I forgot to load a module's include file.

Upon figuring this out, I expected errors, but totally not this:

Notice: Undefined index: comment_confirm_delete in drupal_retrieve_form() (line 670 of /includes/form.inc).

Warning: call_user_func_array(): First argument is expected to be a valid callback, 'comment_confirm_delete' was given in drupal_retrieve_form() (line 705 of /includes/form.inc).

Notice: Undefined index: actions in example_report() (line 122 of sites/all/modules/example/example.module).

Warning: array_unshift(): The first argument should be an array in example_form_alter() (line 669 of sites/all/modules/example/example.module).

The non-existing form was retrieved, prepared, processed, and even submitted/executed! (i.e., $form_state['executed'] == TRUE)

Considering other code in D7, I would have expected a PHP exception.