Hello, saw this logged in the error log in our NginxPlus (nginx/1.7.11 (nginx-plus-extras-r6-p1) load balancer. Any ideas?

2015/09/08 14:31:02 [alert] 2399#0: *452322 zero size buf in output t:0 r:0 f:1 0000000000000000 0000000000000000-0000000000000000 0000000002F51428 0-0 while sending request to upstream