Imagine model:

@Model(className = "Data", targetId="", properties = {
    @Property(name = "s3", type=String.class),
    @Property(name = "p3", type=En.class)
})
final class DataModel {
    private static Data ui;
    static void onPageLoad() throws Exception {
        ui = new Data("A", En.A);
        ui.applyBindings();
    }
    @OnPropertyChange("s3")
    static void s3Is(Data d) {
        System.err.println("s3: " + d);
    }
    @OnPropertyChange("p3")
    static void p3Is(Data d) {
        System.err.println("p3: " + d);
    }
}
enum En {
    A, B
}



and HTML:

<div>
    String:
    <input type="radio" name="s3" value="A" data-bind="checked: s3">Ano
    <input type="radio" name="s3" value="B" data-bind="checked: s3">Ne
</div>
<div>
    Enum:
    <input type="radio" name="p3" value="A" data-bind="checked: p3">Ano
    <input type="radio" name="p3" value="B" data-bind="checked: p3">Ne
</div>

then string version works OK while enum one is broken.