I think I found a bug in how the TaskSeries handles Tasks and the Gannt chart displays them.
I create a Task from say, 4/6/2001 to 4/10/2001.
Add SubTask A from say, 4/9/2001 to 4/10/2001. %complete=0
Add SubTask B from say, 4/8/2001 to 4/9/2001. %complete=100
The graph shows the SubTask A at 100% completion.
If I add SubTask A to the TaskSeries after SubTask B, the graph shows SubTask A correctly at 0& completion.