Strange behaviour for Bar Chart when using timeseries and tick values

When i set a bar chart using timeseries and a default value of 12 dates into tick values, the chart looks like are showing 14 dates. It shows a x line in the begining of the chart and in the end of the chart.
i.e. -> https://codepen.io/luispaulopinto/pen/PeZXxW
Using:
`columns: [`
` ['x1', '2018-03-01', '2018-04-01', '2018-09-01', '2018-10-01', '2018-11-01', '2018-12-01'],`
` ['x2', '2018-04-01', '2018-05-01', '2018-06-01', '2018-07-01', '2018-08-01'],`
` ['data1', 30, 200, 100, 400, 150, 250],`
` ['data2', 20, 180, 240, 100, 190]`
` ]`
AND
`axis: {`
` x: {`
` min: '2018-01-01',`
` type: 'timeseries',`
` tick: {`
` values: ['2018-01-01', '2018-02-01', '2018-03-01', '2018-04-01', '2018-05-01', ........]`
` }`
` }`
` }`

On the other side, when I dont use the tick values and set 12 months and 12 values inside data section, it looks like all good. It doesnt show the first and last x line like the previous chart.
i.e. ->https://codepen.io/luispaulopinto/pen/OZMrGm
using:
`columns: [`
` ['x1', '2018-01-01', '2018-02-01', '2018-03-01', '2018-04-01', '2018-05-01', ....],`
` ['x2', '2018-01-01', '2018-02-01', '2018-03-01', '2018-04-01', '2018-05-01', ....],`
` ['data1', 0, 0, 0, 0, 0, 0, 30, 200, 100, 400, 150, 250],`
` ['data2', 0, 0, 0, 0, 0, 0, 0, 20, 180, 240, 100, 190]`
` ],`