Explanation of ListView in virtual mode

I am experimenting with the ListView in virtual mode. I have data for 64 rows and a visible area for 20 rows. The ListView has 9 columns.

The event handler that sends a ListViewItem includes a Debug.Writeline statement, which I included just to see how .Net is invoking the event handler. To my surprise, there's a very definite pattern. It invokes the handler 12 consecutive times for item #0, then 12 consecutive times for item #1, ..., down to item #19.

What's it doing? Why can't it just accept the item I returned upon the first invocation?

Rick Kucia