mod_dav: resume transfers not working (Apache Users)

All,

Forgive me if I am not asking this question in the right way. If I should post it somewhere else, please let me know.

I have been racking my brain as to why some uploads via webdav are failing to resume. I have some users that are uploading 10GB plus files and are trying to resume them when they have a connection timeout with no success. If there is no timeout on the connection, it works. We see the following:

1) client starts the upload

2) client timeout (we pull a network cable to simulate)

3) partial file on the server

3) client tries to resume with an active network connection

4) client does a PROPFIND for the file on the server and gets a status 404

5) server deletes the file

6) client resume fails and starts over from scratch.

We pretty much have the standard config per documentation on the server...http://httpd.apache.org/docs/2.2/mod/mod_dav.html

I have tried multiple clients that support resume (cyberduck and crossftp). Both state "Some servers may not support resumable transfers and the file will be reloaded instead." What is it specifically that has to be implemented on a server to support resumable transfers?