Binding InputScope with a converter in Windows Phone 8.1

I'm trying to bind the InputScope Value of a textbox on a type. For this I use a converter :

Xaml :

<TextBox 
    Style="{StaticResource TextBoxStyle}"
    InputScope="{Binding Type, Converter={StaticResource typetoInputScope}, Mode=TwoWay}">

Converter :

public class TypeToInputScope : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        Type type = (Type)value;
        if (type == typeof(string))
        {
            return InputScopeNameValue.AlphanumericHalfWidth;
        }
        else
        {
            return InputScopeNameValue.Number;
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        throw new NotImplementedException();
    }
}

When i debug in VS, it goes in the converter, but the InputScope doesn't change.

Ok, here it is :

        public object Convert(object value, Type targetType, object parameter, string language)
    {
        Type type = (Type)value;
        InputScope scope = new InputScope();
        InputScopeName name = new InputScopeName();

        if (type == typeof(string))
        {
            name.NameValue = InputScopeNameValue.AlphanumericFullWidth;
        }
        else
        {
            name.NameValue = InputScopeNameValue.Number;
        }
        scope.Names.Add(name);
        return scope;
    }