Ion-select two-way databinding with an array?

I’m using an ion-select as follows:

    <ion-select [(ngModel)]="usedFields" multiple>
        <ion-option *ngFor="let field of fieldStorage" [value]="">{{ }}</ion-option>

With usedFields as an array of numbers and fieldStorage an array of objects with two properties: ids which are numbers and names which are strings. In addition, I have a button elsewhere which when clicked reads a QR code, reading a number and then pushes it into the usedFields array. So far so good, but the corresponding checkbox in the ion-select doesn’t update; the usedFields array itself is correct, but the ion-select checkboxes are not. Do I have to programatically reload the ion-select checkboxes from the ngModel or something?

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