When classes inheriting RadDocument are exported using XamlFormatProvider, XmlException with message "The prefix 't' cannot be redefined from 'clr-namespace:Telerik.Windows.Documents.Model;assembly=WpfApplication1' to 'clr-namespace:Telerik.Windows.Documents.Model;assembly=Telerik.Windows.Documents' within the same start element tag." is thrown

Similar scenario works with inheriting other elements.

Steps to reproduce:
1. Create an object which inherits the RadDocument
2. Pass the created object as a parameter for the XamlFormatProvider.Export() method
Observe: An XmlException is thrown
Expected: The object to be exported