Ion-chip or ion-button not styled within ngFor

Hi everyone,
I face a problem, ion-chip or ion-button (at least) have no style when used within ngFor. However, ion-avatar and ion-badge are well skinned.

Any advice ?

<ion-grid id="ground-area" *ngIf="ground">
    <ion-row *ngFor="let area of ground">
        <div text-center *ngFor="let pos of area" ion-col>
            <ion-chip ion-col>
                    <img src="{{ pos.key.avatar) }}" alt="avatar">
                <ion-label >{{ pos.label }}</ion-label>
                <ion-badge>{{ pos.count}}</ion-badge>

Ok found !

<ion-chip [class]="foo" ...

without [class] it works fine.