为什么在混合图表上添加时间单位会将第一个栏向左推?

我使用的是混合图表(条形图和两行图)。一切都很好,直到我在x轴上加上时间单位。图表中的第一个栏向左移动。

var data = [
    {
        date: "2014-01-04 22:23:00",
        pop: 20,
        rh: 67,
        temp: 38,
        wspd: 7
    },
    {
        date: "2014-02-04 22:23:00",
        pop: 15,
        rh: 69,
        temp: 39,
        wspd: 8
    },
];

new Chart(document.getElementById("canvas"), {
    type: 'bar',
    data: {
        labels: data.map(d => new Date(d.date)),
        datasets: [{
            label: "RH",
            type: "line",
            borderColor: "#8e5ea2",
            data: data.map(d => d.rh),
            fill: false
        }, {
            label: "Temp",
            type: "bar",
            backgroundColor: "rgba(0,0,0,0.2)",
            data: data.map(d => d.temp),
        }
        ]
    },
    options: {
        title: {
            display: true,
            text: 'Daily Forecast'
        },
        legend: { display: true },
        scales: {
            xAxes: [{
                type: 'time',
                time: {
                    unit: 'month'
                }
            }],
        },
    }
});