UWP CustomRenderer for Checkbox: Pointer over Checkbox changes style?

I'm working with Xamarin.Forms and I made a CustomRenderer for Checkbox in UWP. When I set all the Checkboxes of my items in the ListView to true, the Checkboxes are displayed correctly with the check inside the box

However, if I hover my mouse over the Checkboxes, they immediately change their appearence (the check disappears but it's still selected). In the following screenshot, I moved my cursor over the 3rd - 7th Checkboxes:

This is my overridden OnElementChanged method in the CustomRenderer:

protected override void OnElementChanged(ElementChangedEventArgs<EvaCheckbox> e)
{
    base.OnElementChanged(e);
    var model = e.NewElement;
    if (model == null)
    {
        return;
    }

    nativeCheckbox = new CheckBox();
    CheckboxPropertyChanged(model, null);
    model.PropertyChanged += OnElementPropertyChanged;

    nativeCheckbox.Checked += (object sender, Windows.UI.Xaml.RoutedEventArgs eargs) =>
    {
        model.IsChecked = (bool)nativeCheckbox.IsChecked;
    };

    nativeCheckbox.Unchecked += (object sender, Windows.UI.Xaml.RoutedEventArgs eargs) =>
    {
        model.IsChecked = (bool)nativeCheckbox.IsChecked;
    };

    SetNativeControl(nativeCheckbox);
}

I tried to override the PointerEntered event of nativeCheckbox. It works, for example if I set the model.IsChecked to true on this event, it will be set to true:

nativeCheckbox.PointerEntered += (s, args) =>
{
    model.IsChecked = true;
};

But I don't know how to (if even at this place) prevent the checkbox from changing it's appearance when moving the cursor above the Checkbox. Just leaving the triggered event with empty code like this won't change anything about the described behaviour:

nativeCheckbox.PointerEntered += (s, args) => { };

How can I prevent the Checkbox from changing it's appearance when I move my cursor over it?