Completion percent initialization in Gantt Chart Light Library

I initialize some tasks (GanttChartItem objects) within a Gantt Chart enabled control from Gantt Chart Light Library without setting any completion value, but at runtime I see some completion bars initialized. What happens?

By default, GanttChartItem.CompletedFinish property is set to DateTime.Today. Therefore, if you initialize tasks to be displayed in the past (i.e. their Start property value is set to be in the past, compared to the current date), you should also make sure you set their CompletedFinish property to a value between Start and Finish. If the completion is 0%, you may safely set CompletedFinish to Start value, and if the completion is 100%, you may safely set CompletedFinish to Finish value.

If you want to initialize completion based on existing percent values, you may also use GanttChartComponent.GetCompletedFinish method:

GanttChartItem.CompletedFinish = GanttChartComponent.GetCompletedFinish(start, percentCompleted / 100.0, finish);