@asiacurious
I returned to desk 10 of Jomthien Immigration, the TM30 desk, and pointed out the latest entry used the same visa and same address. The only difference was that I had been in and out. And therefore a fine was not appropriate.
Their clarification was that the fine was correct because the "visa" (Did they mean visa, permission to stay or extension of permission to stay or, in fact, all 3!) was not issued by Chonburi Immigration. If it had been, then there is no requirement to report each entry.
In my case :-
My DTV was issued by the MFA (London Embassy)
My permission to stay was granted by Bangkok Immigration (Suwannaphum Airport)
and I have not extended that permission to stay.
So, Jomthien Immigration's take is the fine stands and every "visa" not issued by them requires a TM30 for each and every entry.