I see disable button on submit is already enabled in advanced settings and I can confirm it works well if a from is called from in a NON-modal dialog.
But for modal dialog add, If i accidentally/intentionally double or triple click, I actually end up with more records after the dialog closes.
And the modal dialog form takes a lot of time to disappear, on slow networks Some users might not know that is actually trying to submit so they end up clicking the submit button over and over again, so you can end up with more records.