steppedline chart stacked with stacked groups does not work properly

[koljagava]

Expected Behavior

Hi there, i would like to separete datasets in 2 different stacked group using stack property option

Current Behavior

stack (group) property for line (steppedLine) chart type does not work

Possible Solution

Steps to Reproduce (for bugs)

here is the example : https://stackblitz.com/edit/chartjs280stackedgroup

stack group 2 (current month data) should start with 1 (as reported by lable) and so for the other current month dates.

Context

Environment

• Chart.js version: 2.8.0
• Browser name and version: Mozilla Firefox 68.0.1