When the iPerf server is run in UDP mode as a daemon it fails to send generate a report and/or send it to the client for display. Frequently the only response is "Warning: Did not receive ack of last datagram after 10 tries". Looking back through the archives this seems to be a problem dating back to at least 2006. It is easily reproducible and renders iPerf somewhat useless in terms of my needs. If this problem will not be fixed please make it clear in the documentation that this combination of modes is not supported. Thanks!
As a note, if you send the server to the background with either ctrl-z and bg or a & it does work as expected.