reverse proxy - PROPFIND 405

I have a reverse proxy pointing to IIS on the backend. The backend web application generates reports in RTF format that the user then displays on their workstation using MS Word or similar application. From the end user's perspective, everything works fine.

However, on the proxy, the access.log is reporting a lot of 405 errors when the report generation is completed:

10.130.21.118 - - [29/Oct/2014:14:49:21 -0700] "OPTIONS / HTTP/1.1" 200 0 "-" "Microsoft-WebDAV-MiniRedir/6.1.7601"
10.130.21.118 - - [29/Oct/2014:14:49:22 -0700] "PROPFIND / HTTP/1.1" 405 1293 "-" "Microsoft-WebDAV-MiniRedir/6.1.7601"
10.130.21.118 - - [29/Oct/2014:14:49:22 -0700] "PROPFIND / HTTP/1.1" 405 1293 "-" "Microsoft-WebDAV-MiniRedir/6.1.7601"
10.130.21.118 - - [29/Oct/2014:14:59:22 -0700] "OPTIONS / HTTP/1.1" 200 0 "-" "Microsoft-WebDAV-MiniRedir/6.1.7601"
10.130.21.118 - - [29/Oct/2014:14:59:22 -0700] "PROPFIND / HTTP/1.1" 405 1293 "-" "Microsoft-WebDAV-MiniRedir/6.1.7601"
10.130.21.118 - - [29/Oct/2014:14:59:22 -0700] "PROPFIND / HTTP/1.1" 405 1293 "-" "Microsoft-WebDAV-MiniRedir/6.1.7601"

I'm looking for any suggestions of how these PRODFIND 405s should be handled. Like I said, the users get their reports as is, but the large number of 405s make me think there's probably a more efficient way to manage the traffic.

Thanks for any help!