SRC-NAT on 2.9rc - dest port not matched?

Anyone see any reason why this will not trigger? (rc10)

add chain=srcnat protocol=tcp dst-port=65001 action=src-nat to-addresses=10.10.10.1 to-ports=0-65535
comment=“” disabled=no

Im trying to change the source ip to the MT itself as it comes into my network so that devices behind it see it coming from the gateway. If I remove the dst-port and change it to src-address and put a single IP it works …

Sam