datagrid layout

[kevin11]

I have a datagrid with a row template with 6 text fields in it. I am trying to display two rows of items, first row has 6 labels, second row has two labels.

Now, for some reason, the handler on LayoutControl pControlRect is invoked 6 times.
Why is this ? pControlRect just seems to contain the rect of the background.
As I have two rows, why isn't this handler invoked just twice ?
As I have 8 text items to display, why isn't it invoked 8 times then ?
is LayoutControl supposed to layout a row, and be called once for each row, or is it supposed to be called for each object inside a datagrid ?