Burndown chart starts before specified date and therefore displays wrong data

This is affecting our ability to upgrade to Jira 4.1 since we would be introducing this new unexplained behaviour which affects all our figures.

Attached a screenshot showing the issue. Notice how the start date is the 3rd September, and yet the graph is displayed from
(I'm guessing) 3 days before that day.

I've tried searching for this but couldn't find any similar issues.