Persistent Port Forwarding?

I needed to "Open" a port (5432) via RT-AC66U v378.54_2 Merlin firmware to support a networked SQL dB.

Worked as expected after adding correct info to "WAN -> Port Forwarding List", setting "Enable Port Forwarding = Yes" and "Applying" the config to router.

But after resetting the "WAN -> Enable Port Forwarding = No", the port appears to remain Open?
Is this normal?

Thanks,
Bob