I've opened an issue about this topic on github https://github.com/owncloud/android/issues/1867
I was reviewing the logs of our dedicated proxy between oc android and windows clients and our oc server and I noticed that the new android client (2.2.0) is duplicating all the DAV requests. Each DAV request is sent to the server without the Authorization header, so the owncloud server answers with "HTTP/1.1 401 Unauthorized" . Then the client repeats the same request, this time adding the Authorization header.
I tested it again without proxy, only sniffing the direct communication between the android 2.2.0 client and demo.owncloud.org , it happens too, so is not related with our proxy neither our oc server