It seems you are using the older version of CanvasJS, the above mentioned bug was fixed in the recent version of CanvasJS (v2.0.1GA), please refer this blog post for more info. Kindly use the latest version of CanvasJS. In case the issue still persists please create a jsfiddle reproducing the issue so that we can look into it and help you out.
___________
Indranil Deo
Team CanvasJS