为什么这只会在第一次调用时增加分数？

Question

复制步骤：

1. 打开http://playclassicsnake.com/play
2. 单击向左，向上或向下箭头键使蛇（绿色方块）移动
3. 将蛇指向食物（红色圆圈）
4. 总得分从0到10
5. 再次将蛇指向食物
6. 总分仍为10

预期行为：

每次蛇的头撞到食物时，分数应增加10。

相关的Javascript：

function StatHandler ( totalScoreSelector, fruitEatenSelector )
{
    this.scoreElem = $(totalScoreSelector);
    this.fruitEeatenElem = $(fruitEatenSelector);

    this.incrementScore = function ( incAmount )
    {
        var that = this;
        $.ajax({
            type: "POST",
            url: "Play/IncrementScore?amount=" + incAmount,
            success: function (newScore)
            {
                that.scoreElem.text(newScore);
                console.log(newScore); // TEST
            },
            error: function ( ) 
            {
                alert("error occured!");
            }
        });
    }
}

        if (game.food.pos.x == newHeadX && game.food.pos.y == newHeadY) // if new head hit food
        {
            this.links.push(new game.elementOnGrid(game.board.rect(oldTailX * game.blockWidth, oldTailY * game.blockWidth, game.blockWidth, game.blockWidth).attr('fill', '#19FF19'),
                            oldTailX,
                            oldTailY
                            ));       // fill space left by trail before it was translated
            // i.e. lengthen the snake
            game.coords[oldTailX][oldTailY] = true; // update coordinate list
            game.stats.incrementScore(10);
            game.placeFood(); // replace food
        }

相关C＃：

public class PlayController : Controller
{

    private ushort score;

    // GET: Play
    public ActionResult Index ( )
    {
        ResetScore();
        return View ( );
    }

    [HttpPost]
    public ushort IncrementScore ( ushort amount )
    {
        score += amount;
        return score;
    }

    [HttpPost]
    public void ResetScore ( )
    {
        score = 0;
    }
}

关于发生了什么的任何想法？