I am trying to read values from document after that the file was edited in Office Web Apps. Problem is, that this document is locked by Sharepoint (SPFile.LockType - Shared). I tried to Check Out and Check In the file and read it afterward, but this "solution" isn't reliable. Sometimes document doesn't contains new values. I think it is related with this issue http://support.microsoft.com/kb/899709/en
This problem also could be due to another person opening the document. Verify that the check out requirement is not enabled on your library. This will prevent multiple users from opening and modifying a document.