Incorrect values for team effort in burndown chart?

I seem to get incorrect values for the team effort in the hour burndown chart. At least the values are different from what I expected. The values are only incorrect for some of the dates.

The attached pdf shows a screenshot of the burndown chart with an indication of the expected hours. It also contains a listing of the worklogs (including the sql query) and the expected hours I calculated.

I assume the team effort should by counted on the bases of the 'start date' of the work logs, not the 'created' or 'updated' date? Is this correct?