AdvancedDataGridItemRenderer systemManager property is NULL

Question

I have an AdvancedDataGrid. Occasionally, when I roll over the cells immediately after changing the dataProvider, I get a null pointer. The null pointer is caused by the systemManager property of the item renderer (AdvancedDataGridItemRenderer) being null so...

ToolTipManagerImpl.createTip() is setting sm to null on line 831

line 831 looks like this:

var sm:ISystemManager = getSystemManager(currentTarget) as ISystemManager;

(currentTarget is an instance of AdvancedDataGridItemRenderer with a null systemManager property)

with sm set to null, the next line (832) fails

sm.topLevelSystemManager.addChildToSandboxRoot("toolTipChildren", currentToolTip as DisplayObject);

and then the errors keep coming...

so, I guess the question is - why would an instance of AdvancedDataGridItemRenderer ever have systemManager == NULL and how can i fix this?