当项目源更改时，WPF ComboBox重置所选项目

Consider the following XAML:

考虑以下XAML：

<ComboBox Name="CompanyComboBox" 
    HorizontalAlignment="Stretch"
    ItemsSource="{Binding Path=GlobalData.Companies}" 
    SelectedValuePath="Id"
    SelectedValue="{Binding Customer.CompanyId, ValidatesOnDataErrors=True}"
    DisplayMemberPath="Name" />
<Com