Issue with angular checkbox: can't uncheck the checkbox

I have the following form control:

<input type="checkbox" name="emailNotification" ng-model="emailNotification.value" class="form-control"/>

which is populated by with a default value as follows:

 $scope.emailNotification = {
            value: emailNotification.data
        };

Now it seems I have a binding issue: the value is true and I can't uncheck the checkbox...

Can anyone please help? What can possibly cause this?