Odd reverse proxy behavior

[nailxx]

Got it!

The problem was absolutely not related to nginx configuration. I found
it when I continued to get 502s even with nginx process down O_o

I've accidentally added two A-records to the DNS-zone with same name but
different IPs. Looks like the resulting IP was chosen in
semi-round-robin fashion. And when a not configured server was chosen,
I've got those 502s.

Whew!… Sorry for disturbing.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,216073,216075#msg-216075