The Control Chart shows data for issues that have been in the status but are no longer selected in the filter column for status. By default, this will include issues that are still moving across the board but the filter is meant to ignore this status.

The horizontal placement indicates when the issue(s) transitioned out of the last status selected on the chart. If an issue has moved from 'In Progress' to 'In Review' and then to 'Reject' and if the filter deselected for 'In Review' and 'Reject'. The issues will still show up that are in 'Rejected' status.

The filter needs a better explanation or the filter should not list the issues from the status that is not selected.