Removing regions, then adding new brings back the removed

Try this:

``` javascript
var chart = c3.generate({
data: {
columns: [
['data1', 30, 200, 100, 400, 150, 250],
['data2', 50, 20, 10, 40, 15, 25]
]
}
});

chart.regions.add({axis: 'y', start: 160});
chart.regions.remove();
chart.regions.add({axis: 'y', end: 40}); // 2 regions now
```

Also, adding an y grid line seems to bring back removed regions.

``` javascript
chart.regions.remove(); // no regions
chart.ygrids.add({value: 150}); // wait, no..now we have 2 again
```

Am i missing something?