Thank you. Unfortunately I can't repeat it against bad12 either:
~/src/curl$ src/curl -v bad12.haxx.se
* STATE: INIT => CONNECT handle 0x19c3438; line 1011 (connection #-5000)
* Rebuilt URL to: bad12.haxx.se/
* Hostname was NOT found in DNS cache
* Adding handle: conn: 0x19fd3b8
* Adding handle: send: 0
* Adding handle: recv: 0
* Curl_addHandleToPipeline: length: 1
* 0x19c3438 is at send pipe head!
* - Conn 0 (0x19fd3b8) send_pipe: 1, recv_pipe: 0
* STATE: CONNECT => WAITRESOLVE handle 0x19c3438; line 1042 (connection #0)
* Trying 18.104.22.168...
* STATE: WAITRESOLVE => WAITCONNECT handle 0x19c3438; line 1103 (connection #0)
* connect to 22.214.171.124 port 80 failed: Connection refused
* Trying 126.96.36.199...
* connect to 188.8.131.52 port 80 failed: Connection refused
* Trying 2a00:1a28:1200:9::1...
* Immediate connect fail for 2a00:1a28:1200:9::1: Network is unreachable
* Trying 2a00:1a28:1:2010::1...
* Immediate connect fail for 2a00:1a28:1:2010::1: Network is unreachable
* Failed to connect to bad12.haxx.se port 80: Connection refused
* Closing connection 0
* The cache now contains 0 members
* Expire cleared
curl: (7) Failed to connect to bad12.haxx.se port 80: Connection refused
We need to pin down exactly which circumstance is triggering it. Can you show me your output against bad12?