There is a post on GB about motorcycle hire.
This was my experience.

My IDL did not cover me to ride a motorbike and when I was pulled over by the police I was told this. Something of an unpleasant surprise. Despite ample opportunity I did not pay him but instead took the ticket and paid it the next day at Na Jomtien police station. Where incidentally they now have a western gentleman who offers assistance (anything confiscated ect).
When I was stopped again I showed the officer the receipt and he just waved me on.
So, is it likely that only one fine is payable for this even if you get stopped again?