NginxPlus error: zero size buf in output

[justink101]

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

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,261516,261516#msg-261516