Unfortunately, there is... 😏 (been explained that last year by immigration officers in a separate room). There are unofficial rules being put in force by those who have power everywhere here in Thailand.
You can just say you'd go by land to Laos or Cambodia afterwards, so no need to buy a ticket. Airlines might ask about it, but as long as you're able to explain this in English to an immigration officer, they let you on the flight without any problem.
I went there at the end of the last month with my visa expiring on 3 May and got a stamp 'under consideration' until 27 May. It might be or it might not be prolong after that.