When I create a firewall rule in NAT table that should masquerade outgoing WAN interfaces (by means of Outgoing Interfaces list), the list is set to the default value when the rule is saved.
To reproduce:
/interface list add name=WAN
/interface list member add interface=ether01 list=WAN
/interface list member add interface=ether02 list=WAN
/ip firewall nat add action=masquerade chain=srcnat log-prefix="" out-interface-list=WAN
