I have a strange problem that I am trying to work through, and I cannot seem to solve it.

Basically I have a grid filling with data and a single column of checkboxes inserted into position 0.  What I want to do is to have the user click on a checkbox to either select or deselect a row.  So far so good.  Now I want to allow the user to select multiple rows in the grid, and when the spacebar is tapped, the checkboxs will toggle.  This is where it gets fun.  I have Row Selectors set to Show; Row Selector Header Style set to Default Behavior; Row Selection set to Extended Select. 

 In code, I am trapping the spacebar in the KeyDown event.  Then for each row that is selected in the Selected.Rows collection I toggle the value in the cell thus:

private void ugSellingTitles_KeyDown( object sender, KeyEventArgs e )
        {
            // Trap spacebar
            if ( e.KeyData == Keys.Space )
            {
                foreach ( UltraGridRow rowsSelected in this.ugSellingTitles.Selected.Rows )
                {
                    if ( ( (bool)rowsSelected.Cells[ "SELECT" ].Value ) == false )
                    {
                        rowsSelected.Cells[ "SELECT" ].Value = true;
                    }
                    else
                    {
                        rowsSelected.Cells[ "SELECT" ].Value = false;
                    }
                }
            }
        }

When I run my app and display the grid, I get a column to the left of my checkboxes that displays a triangle to indicate selection, which is fine.  I can click on the extended selector column and hold down the shift key and click several rows down highlighting a bunch of rows.  Then I can hold the the ctrl key and select additional individual rows.

When I tap my spacebar the first time, all the rows that are highlighted have their checkboxes checked. 

When I tap the spacebar a second time, all of the rows that are highlighted have their checkboxes cleared except for the last row.  It's checkbox is still checked.

When I toggle the spacebar a third time, all of the highlighted rows now have their checkboxes selected again except for the last row, which is now cleared.

When I toggle the spacebar a fourth time, all of the checkboxes are cleared.

When I toggle the spacebar a fifth time, all the checkboxes are set, and if I toggle a sixth time, we are back to all checkboxes being cleared except for the last one which is still checked.

Am I taking the right approach here?  Any ideas about what I could be doing wrong?

Thanks.