Burndown chart showing the incorrect amount of open issues in a milestone

Description of the problem

Burndown chart showing the incorrect amount of open issues in a milestone.

Which Group/Project (with full path) is experiencing the issue?

/ArthurPBressan/OW-event-item-tracker/milestones/1

Approximate date/time when the error occurred.

April 14 2017, throughout the day

Describe what you were doing right before the issue occurred.

I had never used the burndown chart before, and i wanted to give it a try, so I created one and then added issues that were already open to the milestone.