For each UPDATE of the same text, the letter that has accentuation is duplicated

With each update of the same text, accented characters are duplicated.

See in the image below what happens every time I click refresh. As you can see, letters that have some type of accent are duplicated.

Do I make characters with accentuation no longer duplicated?

FormCode:

<?php$painel=mysqli_query($con,"select detalhe_sobre from anuncios where id = '$idcli'");
while($painel_texto=mysqli_fetch_array($painel)){
$texto_empresa = utf8_encode(strip_tags(nl2br($painel_texto['detalhe_sobre'])));
}
?>
<form class="frm-adm-painel" action="gravar-texto.php?cliente=<?php echo $idcli; ?>" method="post">
    <textarea name="textoempresarial" rows="10" placeholder="Texto sobre a Empresa"><?php echo $texto_empresa;  ?></textarea>
    <button type="submit" name="botao">GRAVAR</button>
</form>

Record Code:

<?php
if (!empty($_GET['cliente'])){
    $idcli = $_GET['cliente'];
    $textoempresarial = utf8_encode($_POST['textoempresarial']);
    $painel=mysqli_query($con,"UPDATE anuncios SET detalhe_sobre = '$textoempresarial' where id = '$idcli'");
    header("location: painel.php?cliente=$idcli");
}
?>