TYPO3 Core

I past this HTML in a Plain HTML element :

<form action="" method="post">
<div class="w75 mts">
    <div class="w100 txtcenter category">Demandeur</div>
    <div class="label mtm txtleft">NOM *</div>
    <div><input class="w100" type="text" name="nom"></div>
    <div class="label mtm txtleft">Prénom</div>
    <div><input class="w100" type="text" name="prenom"></div>
    <div class="label mtm txtleft">Téléphone</div>
    <div><input class="w100" type="text" name="tel"></div>
    <div class="label mtm txtleft">Adresse email</div>
    <div><input class="w100" type="text" name="email"></div>
    <div class="label mtm txtleft">Adresse postale</div>
    <div><textarea class="w100" name="adresse"></textarea></div>
    <div class="mtm txtcenter"><button class="medium green awesome">Valider</button></div>
</div>
</form>

I save and, when I want to edit the code, the text is cut after the <textarea> element and the rest of the form appears below the textbox :

This is a fresh install of Typo3 6.0.4