InfoPath supports forms with file attachments by encoding the attachement as base64 and including the following PI

<?mso-infoPath-file-attachment-present ?>

at the top of the XML document to indicate that a file has been attached to the document.

WSS adapter works with InfoPath forms with attachements by making sure that it does not add/remove/update any of the PIs that are related to file attachment. If the files are attached to the form in InfoPath then the PI should be