当修改基础属性值时，文本框插入符号会出错

See the following example:

看下面的例子:

<Window 
  xmlns="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="https://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:src="clr-namespace:WpfApplication1"
  SizeToContent="WidthAndHeight">
  <Window.DataContext>
    <src:CodeName/>
  </Window.DataContext>
  <TextBox Text="{Binding Code, UpdateSourceTrigger=PropertyChanged}" />
</Window>
<Window