Comment # 7 on bug 1222338 from Dirk Mueller

I've attached the log with ZYPP_MEDIA_CURL_DEBUG=2 set. I can reproduce inside
a tumbleweed container as well, the missing piece was 

techpreview.ZYPP_MEDIANETWORK=1

in /etc/zypp/zypp.conf

turning off medianetwork as well as downgrading curl avoids the issue.