When adding tickets to a sprint, if there is previous work done on the ticket in a specific order, the time added to the sprint is not what is expected. The following is how you can reproduce the issue.

I suggest that you leave 1-2 mins between each to ensure different time stamps

1. Create a new issue
2. Log some work on it
3. Log some more work on it
4. Add it to an active sprint
5. Go back and edit the first work log to change the remaining hours
6. View the burndown report for the sprint

At this point you'll see that the time that is added to the chart does not align with what you'd expect.

The last action of logging work should have set the RTE to a specific value. That is the value that is expected when adding the issue to the sprint. If the RTE is changed after adding the issue to a sprint then the RTE change should show on the burndown versus changing the original addition to the sprint.