Hi,
enable firewall;
disable: SPI, DoS, Block Wan, Rem. Management
and remove all custom Access rules (Restore to default rules).
probably enable the firewall and set a pass-all rule.
It is a bit odd, but it seems to be the only way to disable remote management.
----
Info:
From the manual of recent version, where screenshots of v3 with recent firmware are presented, it seems that they have fixed the behavior.
By default if firewall is disabled, also remote management.
Regards
Hope it Helps.