I created a function for updating GridView column headers for a list and call it whenever the window is re-sized or the listview updates it's layout.
public void correctColumnWidths()
{
double remainingSpace = myList.ActualWidth;
if (remainingSpace > 0)
{
for (int i = 0; i < (myList.View as GridView).Columns.Count; i++)
if (i != 2)
remainingSpace -= (myList.View as GridView).Columns[i].ActualWidth;
//Leave 15 px free for scrollbar
remainingSpace -= 15;
(myList.View as GridView).Columns[2].Width = remainingSpace;
}
}