Epic burndown chart doesn't include issues that have the epic link populated at issue creation time

Issue Summary

Epic burndown chart doesn't include issues that have the epic link populated at issue creation time.

Steps to Reproduce

1. Create an epic.
2. Create an issue in the epic. Make sure that you populate the epic field when you create the issue.
3. Create a sprint. Put the newly created issue in the sprint and start the sprint.
4. Move the issue to done and complete the sprint.
5. Go to the Epic Burndown chart.

Expected Results

The issue shows up on the Epic Burndown chart and is also present in the 'Completed Issues' section.

Actual Results

The issue doesn't show up in the Epic Burndown.

Workaround

If you change the epic link (move to another link and then back to the epic), the burndown report will be fixed, showing the correct story points.