Cache: handling of cache files with long headers. There are two possible situations which can lead to this: response was cached with bigger proxy_buffer_size value (and nginx was restared since then, i.e. shared memory zone content was lost), or due to the race in the cache update code (see [1]) we've end up with fcn->body_start from a different response stored in shared memory zone. [1] http://mailman.nginx.org/pipermail/nginx-devel/2011-September/001287.html