strange focus rectangles on wpf radiobutton

Question

Why does the rectangle appear in the radio buttons when one of them is clicked.

the XAML markup is given below

<RadioButton GroupName="LabelDisp" IsChecked=".. Converter={StaticResource enumBooleanConverter}, ConverterParameter= LabOnly}" Content="{x:Static resx:StringRes.RadioButtonLab}" Style="{StaticResource ListOption}" Command="{Binding Path=Command}"></RadioButton>
<RadioButton GroupName="LabelDisp" IsChecked=".. Converter={StaticResource enumBooleanConverter}, ConverterParameter= DescOnly}" Content="{x:Static resx:StringRes.RadioButtonDesc}" Style="{StaticResource ListOption}" Command="{Binding Path=Command}"></RadioButton>
<RadioButton GroupName="LabelDisp" IsChecked=".. Converter={StaticResource enumBooleanConverter}, ConverterParameter= LabAndDescr}" Content="{x:Static resx:StringRes.RadioButtonBoth}" Style="{StaticResource ListOption}" Command="{Binding Path=Command}"></RadioButton>

Answer 1

I was returning null should have returned Binding.Donothing instead.

public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
            {
                return (bool)value ? Enum.Parse(targetType, parameter.ToString(), true) : Binding.DoNothing;
            }

Answer 2

Those are called FocusVisualStyle, you can remove it -

<RadioButton FocusVisualStyle="{x:Null}"/>

Update

Yeah H.B. is right, i thought you was talking about dotted border we got on clicking radioButton. But it seems a validation border, check your converter code, something is breaking in it.

Answer 3

Looks like a validation error to me, possibly because of the spaces at the front of the ConverterParameter. (You might want to consider using another method for binding RadioButtons)