The problem is that in the CurrentCellEditingComplete event, the current cell is in the state of deactivating. This poses a problem if you try to increase the row count at this point, because that initiates another deactivating call.
One work around available in Version 1.5 is to lock the currentcell while you increase the rowcount. This will avoid the second deactivating call.
private void gridControl1_CurrentCellEditingComplete(object sender, System.EventArgs e)
GridCurrentCell cc = this.gridControl1.CurrentCell;