Some functions like give_pointer_to_obstacle_with_label crash the game on failure even though it's relatively easy to trigger failure. For instance, if the town teleporter is removed from the town, then a play test is started and Tux tries to leave the town, the game will crash because the teleporter doesn't exist anymore. In this particular case, that is caused by the Lua code which is run when exiting the level, so the error isn't even found by the level validator. It might be nice to avoid a hard crash or at least perform some sort of "emergency save" in order to avoid losing work.