Knockout.js two-way binding for checkbox not working

I'm new to knockout.js and I have some trouble with two-way binding of a checkbox.

I have a table that's bound to a list of "companies".

<table>
    <thead>
        <tr>
            <th>...</th>
            <th>...</th>
            <th>...</th>
        </tr>
    </thead>
    <tbody data-bind="foreach: companies">
        <tr>                
            <td>...</td>
            <td><input type="checkbox" data-bind="checked:isCompanyForCommunication, click:$root.checkedNewCompanyForCommunication" /></td>
            <td>...</td>
        </tr>
    </tbody>
</table>

But there should only be 1 company with isCompanyForCommunication = true in the table. So when another checkbox is checked, I have to set all other companies to isCompanyForCommunication = false. Therefore I created a method in the viewModel to uncheck all other companies.

    // Definition of Company
    var Company = function (crmAccountObject, contactId, companyForCommunicationId) {

        this.isCompanyForCommunication = ko.observable(false);
    }

    // Definition of the ViewModel
    var ViewModel = function () {
        var self = this;

        // ...

        // Lists
        this.companies = null; // This observableArray is set somewhere else

        // Events
        this.checkedNewCompanyForCommunication = function (company, event) {

            // Set all companies to False
            for (var i = 0; i < self.companies().length; i++) {
                self.companies()[i].isCompanyForCommunication = ko.observable(false);
            }

            // Set the "checked" company to TRUE
            company.isCompanyForCommunication = ko.observable(true);
            return true;
        }
    }

However, the changes are not reflected in the HTML page. All other checkboxes remain checked.

I created a simplyfied example in jsfiddle to show what exactly I want to achieve with the checkbox http://ift.tt/1IwP3gH

Someone has any idea what I'm doing wrong? Thanks in advance!