wpf - WPF TextBox with IsReadOnly property set to true can still be edited

Question

I'm using a TextBox and for some reasons it needs to be Read Only. I won't argue the reasons here. I know I can use TextBlock or Label to display non-editable content, but in that case, unfortunately, there are TextBox.

<TextBox IsReadOnly="True" Text="{Binding totalAmount, Mode=OneWay, StringFormat={}{0:C2}}" TextAlignment="Right" />

Is anybody know if there is a known issue with it? I'm using WPF 3.5