Hi,
The problem you've encountered is the following:
- When the form is opened from DAT, DBXL is able to automatically detect which doctype it belongs to, and therefore submits to that doctype.
- The form, opened from a file share, is not connected to a doctype, though it has a DBXL submit data connection.
I believe the solution is to declare the doctypename in the submit data connection. Steps 2-3-4 in this document explain how to declare the doctypename.
http://www.infopathdev.com/files/folders/integration_with_sharepoint/entry74101.aspx
Hope this helps!