SaveFormat WordML Error

We have recently purchsed the component and have many documents stored in WordML format. Many of the documents work fine when I use the component, but we also have a fair few that seem to open ok using the component, but when I then try and save it again in the same format I get the following error:
“Unknown object in memory storage”
We are using version 5.1 of the component.
Incidentally if after opening the WordML file I try and save as ‘doc’ format, it appears to save ok.
Any help would be appreciated.
I have attached a sample document that we are having trouble with. The code I use is:

Document cj = new Document(@"f:\temp\dear.xml",LoadFormat.WordML,string.Empty);
cj.Save(@"f:\temp\dear_new.xml",SaveFormat.WordML); // this generates the error

Thank you in advance

Thanks for your reporting this to us. I managed to reproduce problem. I have created new issue #4858 in our defect database. I will notify you as soon as it is fixed.
Best regards.

The issues you have found earlier (filed as 4858) have been fixed in this update.