Uncaught TypeError: Cannot read property 'pageX' of undefined on line charts

[mussrya]

This looks to be a similar bug to the previous #22 but relates to the line chart.

You can see the issue on the official demo page here, if you select the line chart and then hover over to see a tooltip the error will be shown in console:
http://plnkr.co/edit/T9J7bz?p=preview