Close and start sprint date affecting Burndown Chart graph

Summary

When you close a sprint and at the following seconds you start the new sprint, JIRA understands that you have started the new sprint some seconds after the previous sprint closure. This can reflect in Burndown Chart showing a bunch of issues added to the sprint shortly after it began.

Steps to Reproduce

• Close Sprint_A at Wed May 31 2017 10:25;
• Wait some seconds;
• Start Sprint_B at the same minute (Wed May 30 2017 10:25);

Expected Results

• Complete date and start date registered in JIRA with the exact time these actions occurred.

Actual Results

• Complete date for Sprint_A shows in the database as
  Wed May 31 2017 10:25:14 and start date for Sprint_B shows in the database as Wed May 31 2017 10:25:10. In other words, the closed sprint is registered as completed 4 seconds after the new sprint starts;
• Burndown Chart graph shows a bunch of issues added to the sprint shortly after it began.

Notes:

This also occurs if using a custom start time that occurs within a min of the previous close or a time period before the previous sprints close time.

Workaround

As a workaround, you can start the new sprint in the next minute after the sprint closure.