Currently, the information for the document revisions while Track Changes is enabled, is only saved in Xaml
format. If you are using any other format, the this information will be lost. We are planning to add support for export/import tracked changes in Docx format in the 2012 Q2 SP1 release which will be out in a few weeks.
I hope this information is helpful. Please don't hesitate to contact us again if you have more questions or if you are using the XamlFormatProvider to save your documents - in this case there is probably a bug in the format provider and we will need to investigate it.
the Telerik team