relevant parts of Orientation.java to broken ladders:

//near the top
private static final Method _isLadder;

//in the middle somewhere
 public static boolean isClimbable(World world, int i, int j, int k) {
      int blockId = world.getBlockId(i, j, k);
      return _isLadder == null?isLadderOrVine(blockId):blockId > 0 && ((Boolean)Reflect.Invoke(_isLadder, Block.blocksList[blockId], new Object[]{world, Integer.valueOf(i), Integer.valueOf(j), Integer.valueOf(k)})).booleanValue();
   }

//near the bottom
static {
_isLadder = Reflect.GetMethod(Block.class, new Name("isLadder"), false, new Class[]{World.class, Integer.TYPE, Integer.TYPE, Integer.TYPE});
}