DataGrid forgetting selection when inheriting DataGridTextBoxColumn to select a whole row when a cell is clicked

[Rickard Liljeberg]

public class RegularColumn : DataGridTextBoxColumn
{
private int SelectedRow = -1;

protected override void Edit(System.Windows.Forms.CurrencyManager source, int rowNum, System.Drawing.Rectangle bounds, bool readOnly,string instantText,bool cellIsVisible)
{
SelectedRow = rowNum;

this.DataGridTableStyle.DataGrid.Select(SelectedRow);
}
...

This works fine so far that when i click a cell it selects the entire row. So far so good.
But if i click another cell on another row i want that selected aswell... but when Edit is entered the next time the DataGrid has completely forgot the last selection and says that nothing is selected.
So i get a single-select datagrid when iwant a multiselect.

It works if i dont inherit Edit and instead use the RowHeader to select but i dont want to have a RowHeader thats why i want this solution to work.

//Rickard