[flexcoders] How to remeasure itemRenderer

[Amy]

I want to add something to an itemRenderer in a List that will make it 
taller.  I've set the List's variableRowHeight to true.

However, when I set invalidateSize() in my click handler, the measure() 
method never happens.

I've stepped through the code in the debugger, and narrowed it down to 
line 4487 (itemRendererToIndices protected function):

if (!item || !(item.name in rowMap))

When that line runs, the invalidateSizeFlag on item (my renderer) 
suddenly goes to false.

Any idea what's happening?  What is the recommended way to remeasure an 
itemRenderer?

Thanks;

Amy