title: Add items to DataGridViewComboBoxColumn in DataGridView during runtime
body: <p>I'm creating a DataGridView with a column DataGridViewComboBoxColumn. Initially the combo box Items is filled with values using Items.Add("sometext").</p>
  
  <p>Further values are added to the DataGridViewComboBoxEditingControl returned in the event EditingControlShowing of DataGridView.</p>
  
  <p>Hereafter I can correctly select values added initially, but if I try selecting one added later an exception with message "DataGridViewComboBoxCell value is not valid." is thrown.</p>
  
  <p>Any ideas why?</p>