I troubleshot a problem when a wrong content type value was displayed for a new document in document library with multiple content types. Content type “Electronic Letter” was created a while after content type “Letter” and used the same template MS Word 2007 document. The root of the problem was in the document template itself. It was taken from content type “Letter” and contained this content type metadata and when I tried to use it in other content types it still had the original binding to “Letter”. Microsoft says that this problem happens with Office 2007 document only and recommendation is to keep the master copy of the document template on disk and never take it from SharePoint. In my case the problem was that I did not have the master copy on my disk and could only use the document already loaded to SharePoint and bound to the other content type. And finally I found the way how to detach the document.
Open the document from disk and go to Prepare->Inspect Document menu item.
Check “Document Properties and Personal Information” item and press “Inspect” button.
Press “Remove All” button against “Document Properties and Personal Information” item. This will remove all the content type binding of this document.
Press “Close” button and save the document.
After that you can use this document as a master copy for all the other content types where it is used as a template.