Angular2 object property typed as "number" changes to string

I have a very simple Angular2 app running locally. I'm using a service to send an instance of an object to a webservice API. The API validates JSON against a schema, and ID's must be numbers (i.e. NOT quoted in the JSON).

My problem is that when I try to send the object to the webservice, my ID field has quotes around it, even though it's typed to be a number in Typescript.

The behaviour is only observed when the nameproperty of the object contains "special characters".

I've tested and found that it doesn't seem to be the JSON.stringify I use — please see code below.

The app is written in Typescript.

Unit class:

export class Unit {
    id: number;   // This is the problem child
    name: string; // This is the string that can contain special characters
    short: string;
    triggers_plural: number;
    is_headline: boolean;
}

Method to save:
My code for saving an instance of Unit to the webservice:

updateUnit(unit: Unit): Promise<Unit>
{
    var objSend = {unit_data: [unit]};          // Webservice expects an array of units

    console.log(objSend.unit_data[0].id === 2); // Yields false when ID is 2
    console.log(objToReturn);                   // Logs ID to verify it is 2 when testing

    // Code for actual request
    return this.http.put(`${this.unitUrl}/${unit.id}`, JSON.stringify(objSend),{headers:this.headers})
    .toPromise()
    .then(()=> unit)
    .catch(this.handleError);
}

When running the code and calling the method, the console will log that the ID is NOT equal when the Unit object's name property contains special characters.

Example without special characters (no problem, id is a number):

Example WITH special characters (eek! Id is a string!):

The updateUnit method is called from my unit-detail component where you can edit a unit:

export class UnitDetailComponent implements OnInit {
    unit: Unit; // this.unit later on

    constructor(
        private unitService: UnitService,
        private route: ActivatedRoute
    ){}

    ngOnInit(): void
    {
        this.route.params.forEach((params: Params) => {
            let id = +params['id']; // The routing will give id to look for
            this.unitService.getUnit(id)
            .then(unit => this.unit = unit); // Here the unit is instanciated in the first place
        });
    }

    save(): void
    {
        this.unitService.updateUnit(this.unit).then(this.goBack); // Here is the call to updateUnit method
    }
}

It's bound to an input in the template:

<div *ngIf="unit">
    <div>
        <label>Edit unit</label>
        <div>
          <input type="text" [(ngModel)]="unit.name" />
        </div>
    </div>
    <button class="btn btn-default" type="button" (click)="save()">Save</button>
</div>

Maybe the problem arises already when the two-way data binding is filling in the name property when you write something in the <input> but I don't understand how the type of the id can change?

Link to github repos of the whole project: https://github.com/djoike/ng2-cookbook/tree/master-so