I also founded NGIX disabled keep-alive for safari.

I am not sure exact reason of this.

### ngx_http_core_module.c
if (r->keepalive) {

if (r->headers_in.msie6) {
if (r->method == NGX_HTTP_POST) {
/*
* MSIE may wait for some time if an response for
* a POST request was sent over a keepalive connection
*/
r->keepalive = 0;
}

} else if (r->headers_in.safari) {
/*
* Safari may send a POST request to a closed keepalive
* connection and stalls for some time
*/
r->keepalive = 0;
}
}