[flexcoders] data reading for charts inconsistent with Dates?

[netdeep]

I am pulling in data for drwaing on a chart.  My data formerly displayed 
properly, but when 
the data set changed, it no longer displays properly.  I can see the data in a 
dataGrid so I 
know its there:

<mx:DataGrid dataProvider="{axis2.data}" width="400">
          <mx:columns>
         <mx:DataGridColumn dataField="point1" width="300" />
         <mx:DataGridColumn dataField="point2" />
      </mx:columns> 
        </mx:DataGrid>

axis2.data is an ArrayCollection
point1 is a Date
point2 is a Number

But with charts, the display gets flaky.  I can get it to show up in an Line 
chart, but not in a 
Plot chart.  I'm wondering if it is failing to see the Date object. But then 
why does it work in 
the Line chart?  What in the data would cause the entire chart to choke?