It works with the IP address after @. The only time it gives error in my case is when the proxy is listed in the Route header

Thanks,

I have seen this problem as well I thought it was just me. It seemed to be related to using IP addresses after the @ instead of a hostname after the @. It was happening to me when I was trying to REGISTER. When I used the hostname instead of IP address after the @ the problem went away. This does look like some kind of bug, because both should work.