At the end of the Cave to Sealed Gate, when the cave-in occurs, usually one less rock falls than the developers intended. This is triggered by bringing four party members with you (which most will do, of course). If you bring less than four party members, the correct number of rocks will fall instead.
I recall hearing that the reason this happens is because the enemy Kefka counts as a character in your party at the time (as Terra is temporarily removed for the scene). I don't know if that's true. If it is so, would it be difficult to fix the bug by removing the temporary Kefka from the party before the cave-in occurs? How hard would that be for a bug fixing expert to fix?
We have EVEN MORE themes now, but some old ones are gone...