Summary

Although we allow users to start Sprints with a Start Date in the past, that information isn't recognized in reporting.

Steps to reproduce

1. create a new Sprint and add Issues to it;
2. start the Sprint - pick a Start Date in the past;
3. see the Burndown Chart and the Sprint Report - no Issues are considered to be in the original scope, and all appear as added at the moment when the Sprint was actually started.

Expected behaviour: intuitively, one could assume that the selected Start Date will be resembled in reporting.
At the same time, Issue history does include the information that they were added to the Sprint after the Start Date, so technically, the report is right.

This could be addressed with one of the two solutions:

• make reporting recognize past Sprint Start Dates as the dates when Issues were added to Sprints;
• disable the option to set the Start Date in the past altogether.