1) Turn off the OleDataSource flag in the ControllerOptions property of the grid.
2) Try handling QueryColWidth and explicitly set the last col's width there.
this.gridControl1.Model.QueryColWidth += new GridRowColSizeEventHandler(grid_QueryColWidth);
private void grid_QueryColWidth(object sender, GridRowColSizeEventArgs e)
{
GridControl grid = this.gridControl1;
if(e.Index == grid.Model.ColCount)
{
e.Size = grid.ClientSize.Width - grid.Model.ColWidths.GetTotal(0, grid.Model.ColCount-1);
e.Handled = true;
}
}