Add not understandable classes when change ion-input value

Ionic Framework ionic-v3
1

Hi all ! Could any one help please! My login form breaks down, add any css classes to my ion-item, when I try to change or add value to the input. I do not understand why my form is breaks down.

  <ion-list class="list_login">
  <form #loginForm="ngForm" novalidate>
      <ion-item>
        <ion-label floating primary>username</ion-label>
        <ion-input [(ngModel)]="loginData.username" name="username" spellcheck="false" #loginData.username="ngModel" type="text" value="" required></ion-input>
      </ion-item>
      <ion-item>
        <ion-label floating primary>password</ion-label>
        <ion-input [(ngModel)]="loginData.password" name="password" spellcheck="false" #loginData.username="ngModel"   type="password" value="" required></ion-input>
      </ion-item>
      <div>
        <button ion-button class="btn-login" (click)="login(loginForm)">Next</button>
      </div>
  </form>
  </ion-list>