SZ-100 changes its addres in remote AP from external to internal

unknown

At first, I connected remote AP (behind NAT) to a SZ-100 (connected with external IP) - everything works fine.
The next step - put the SZ behind NAT and open all ports according to manual. AP connects, gets configuration, then heartbeat is lost and AP disconnects. 
I connected to AP via SHH and in AP settings I discovered that the controller address has changed from external a.b.c.d to its internal 192.168.xx.xx. So the controller changes this setting by itself, when gives the config to AP? 
How can I solve this?
Thanks in advance.

unknown

You must upgrade F/W 3.1.1.x.

It's solved by control nat ip.

regards.