**Reproduction of the problem**

ng2-charts is a port & modification of Chart.js component for Angular 2. Sometimes the issue is related with Chart.js instead of ng2-charts.
To confirm, if the issue shows in a pure Chart.js project, it is a issue of Chart.js.
Pure Chart.js starting template: https://jsfiddle.net/Hongbo_Miao/mvct2uwo/3/

If the issue does not show in a pure Chart.js project, and shows in a ng2-charts project, please try to provide a minimal demo of the problem.
ng2-charts starting template: http://plnkr.co/edit/Ka4NXG3pZ1mXnaN95HX5?p=preview
