on ED Visa it was a problem to leave the country while you should be "at language class". So they assumed that you weren't actually going to class, but were just using your visa to stay longer as a tourist. That often led to them cancelling the visa. But thats not a problem with DTV.
I had the same situation for an extension. I had to do the new TM30 first, had to pay a pretty solid fine (1600THB or smth like that for 2month overdue) and after that I was allowed to do the extension. Not exactly the same, but the officer were pretty strict in Jomtien.