The Use Case
The user of a form can click on the submit button over and over causing the form to submit. This can be problematic if you only want one click, but it allowed per the W3C spec for a submit.
How to Solve
If you are worried about the end user clicking over and over, then hide the button when you click it.
Set a variable when you click (per the button config) and set the visibility to hide the button.
Optionally, I would also show a different message that says processing so the end user knows that the task is submitted.