Angular toggle variable in ng-click doesn't work

I have a table that lists customers, and for customers that also have a list of customers, the user can click on the table row to display that list. HTML looks like this:

        <tbody ng-repeat ="item in customers | clientSettingsFilter:customerId">
            <tr ng-class="{'row-hover': item.clientSettings.length>0}" ng-click="item.showClients=!item.showClients">
                <td><span ng-class="{true:'glyphicon glyphicon-chevron-down', false:'glyphicon glyphicon-chevron-right'}[item.showClients]"  ng-hide="item.clientSettings.length==0"></span></td>
                <td>{{item.id}}</td>
                <td>{{item.name}}</td>
                <td><button type="button" class="btn btn-default btn-xs" ng-click="go('/client-config/defaults/'+item.id)">Defaults</button></td>
            </tr>
            <tr ng-show="item.showClients">
                 ..... // client data

My weird behavior is this:

If I don't define the 'showClients' property in the customers dataset, everything works as expected, but the chevron icon is not displayed at first. After one click, it shows up and the toggle works as expected. I thought it might be because ng-class is looking for true or false, and undefined doesn't satisfy both.

If I predefine the showClients property to true or false, the chevrons are displayed correctly on page load and the client list is displayed correctly, but the toggle doesn't work anymore, like ng-click doesn't do anything or fails for some reason Change the value. I'm not sure how to debug inline directives like this.

edit

As requested, here is the relevant event code from the controller:

filter('clientSettingsFilter', function () {
    return function (customers, customerId) {
        var filtered = [];

        if (!customerId)
            return filtered;

        customerId = customerId.toLowerCase();

        angular.forEach(customers, function (item) {
            if (item.id.toLowerCase().indexOf(customerId) !== -1) {

                // format some text properties, omitted for brevity

                // if this line is uncommented, the ng-click does not work
                //item.showClients = false;
                filtered.push(item);
            }
        });

        return filtered;
    };
});