The whole idea is that the form builder carries forward the action that was clicked originally for you. That's the only way we can know which action to execute in the end.
What do you need to know?
Do you need to distinguish OK and Cancel? If cancel is hit, you won't even reach the submit blocks of ad_form/form is_valid will not be true.
If you need to distinguish between the original action button click and the OK button click, again clicking an action will not set form is_valid.