Expression has changed after it was checked during iteration by map keys in angular 2

I don't understand why I get error. My map is not changed .

Expression has changed after it was checked. Previous value: '[object Map Iterator]'. Current value: '[object Map Iterator]'

<tr *ngFor="let author of bindedAuthors.keys()"><td> {{author}}</td><td><button (click)="onUpdate(author)"            class="btn gl-btn-primary">Update</button></td><td><button (click)="onDelete(author)" class="btn gl-btn-default">Delete</button></td></tr>

The result is expected, all data is shown but this error is flooding the console every time.