Textbox.Focus() problem. Repeats SQL by focusing on the field

Question

I have a function that records some information in a table when leaving a TextBox (Leave). But when leaving, the focus returns to the first TextBox. When this occurs it directs the focus as it should, but reinserts the line in the bank with the same information (duplicates). What can I do to adjust?

I’m doing it this way:

public void InsereDados()
    {
        //Pega o valor dos campos e insere no banco
    }

    public void AtualizaGrid()
    {
        //Atualiza as informações no Grid        
    }

    private void Tbnome_Leave(object sender, EventArgs e)
    {          
            InsereDados();
            AtualizaGrid();
            //Volta o Foco para o Primeiro TextBox
            TbCod.Focus();           

    }