Images not loading sometimes with NGINX as RP

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Hello NGINX users and devs,

it's not the first time now, that I have the problem that some images
are just not loading sometimes (only after a few refreshes, gif images
in this case) with NGINX as reverse proxy. I haven't figured out yet
why, I've had this problem with the old 0.x branch a few years ago, even
with the default config and now I have the same problem with the 1.x
branch and an advanced config with caching enabled (doesn't matter if I
enable or disable it, have already tried that). Has anyone had the same
problem before or has a clue why that could be?

Greetings

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,223791,223791#msg-223791