How to remove wpf grid sort arrow after clearing sort descriptions

c#, c#-4.0, sorting, wpf, wpfdatagrid

Solution

simple solution i can think of is

foreach (DataGridColumn column in DataGridView.Columns)
{
    column.SortDirection = null;
}

Problem

I click on a grid header to sort a column and then click a "Reset" button to clear the sort descriptions through its collection view. But the sort arrow icon still persists in the header. How to remove it?

Original source