Toggling off bar series, then loading data with unload: true, shows bar series again

[dayvidwhy]

• C3 version: 0.6.3 (or whatever the sample documentation uses)
• D3 version: v5
• Browser: Chrome 74
• OS: MacOS

I'm having an issue where if you have a bar chart with two series, and toggle one of the series to be hidden, and then load more data, the hidden series comes back, appearing on top of/or behind the other series.

You can reproduce the issue with this snippet of code I modified from one of the samples

var chart = c3.generate({
    data: {
        x: 'x',
        columns: [
            ['x', '2013-01-01', '2013-01-02', '2013-01-03', '2013-01-04', '2013-01-05', '2013-01-06'],
            ['data1', 30, 200, 100, 400, 150, 250],
            ['data2', 130, 340, 200, 500, 250, 350]
        ],
        type: "bar"
    },
    axis: {
        x: {
            type: 'timeseries',
            tick: {
                format: '%Y-%m-%d'
            }
        }
    }
});

setTimeout(function () {
    chart.load({
        unload: true,
        columns: [
            ['x', '2013-01-01', '2013-01-02', '2013-01-03', '2013-01-04', '2013-01-05', '2013-01-06'],
            ['data1', 130, 300, 200, 300, 150, 250],
            ['data2', 130, 240, 300, 400, 250, 350]
        ]
    });
}, 5000);

If you copy paste this into https://c3js.org/samples/timeseries.html

After you paste the code in, hide data1 series by clicking it in the legend.

Wait until the load happens, and you see that the blue bar comes back.

Is this the intended behaviour?

If you remove the unload: true from the second code block, it doesn't happen.