PD error when calling backend API

Hello All,
I’ve below configuration

mode http
log global
option httplog
option dontlognull
option http-pretend-keepalive
option forwardfor except
option redispatch
retries 3
timeout http-request 100s
timeout queue 1m
timeout connect 10s
timeout client 1m
timeout server 5m
timeout http-keep-alive 10s
timeout check 10s
maxconn 10000
#no option httpclose

On same machine, there is tomcat 8.0.33 & APIMAN(an open source API Gateway solution).
We are using haproxy as a proxy to APIMAN, not for any load balancing as we want to hide API endpoints of APIMAN.

When APIs are invoked, 200 OK response code seen without any response message body. haproxy log contains "- PD-- 2/2/0/0/0 0/0"
An example of haproxy log message

Jan 31 08:19:33 localhost haproxy[5969]: xxx.xx.xx.x:61191 [31/Jan/2017:08:19:31.993] main keyServer/keyServer 0/0/0/1665/1665 200 1917 - - PD-- 2/2/0/0/0 0/0 “POST /testaccount/myapi/login HTTP/1.0”

Would appreciate your inputs if you know what I’m missing. Why “PD” error?