Thats a very valid point. There was a very nice man on here who seems to know what he's talking about (in the airline business) and advised to contact the airline direct and ask about their policy on this. the safest bet is to book a cheap flight out of thailand (you can get an air Asia flight to KL for around 800thb) within the 30 days.
So, if you don't have much visa history in Thailand, suggest visa exempt (30 days) with extention at Samui 1900thb (30 days). Need a couple of passport photos each and copies of passport. Get the form at immigration.
For the moment it will, that will change in the near future though. Having the visa is No guarantee that you will be allowed in to the Kingdom. The IO has the final say. The IO has access to all previous entries in to Thailand. But who knows, could get lucky. Time to consider a more appropriate visa perhaps.