Sorry, I don't have any document or SK. This information was provided by our local SE. IMHO, it is logical, how IA API works. But we didn't find any related information on how IA API works when you have mgmt/data plane separation. TAC didn't help.
And from the real gateway: when you switch to dplane and try to find what process listen on port 443, the output will be empty. When you switch to mplane, your output looks like this:
[Expert@fw:mplane]# netstat -tnap|grep 443
tcp 0 0 0.0.0.0:443 0.0.0.0:* LISTEN 12740/httpd2
And when you try to telnet to port 443 on any interface from the data plane, gw will return what you need.