Angularjs validation does not work very well

Question

I have a form where it is shown inside a modal, used by the Bootstrap framework, and because of that, the angular validation does not work right. Only some fields are validated and still yes randomly.

An example, I have in this form three fields: Name, Surname & Email. Sometimes the email field is validated and the name too, if I close the modal, these fields are no longer validated. And so it goes.

Would anyone have any tips that could solve this?

The validations are as follows: Email has to be email type and required field Name and surname fields have to be mandatory only.

The code of my form:

          <form class="ui form" name="add_usuario">
            <div class=" required field">
                <label>Email</label>
                <input type="email" ng-model="email" name="email" required>
            </div>
            <div class="required field">
                <label>Nome</label>
                <input type="text" ng-model="nome" name="nome" required>
            </div>
            <div class="required field">
                <label>Sobrenome</label>
                <input type="text" ng-model="sobrenome" name="sobrenome" required>
            </div>
            <div>
               <button class="ui blue ok button" ng-class="{'loading': enviando}" ng-disabled="add_usuario.$invalid || enviando">Salvar</button>
            </div>
        </form>

It is worth remembering that this validation only does not work when it is inside the modal, be put it directly on the page, this validation works without any problem.