Connection closed when npf restarting with rules in non-default group

Consider the nfp rule definitions below.

     group default {
       block all apply "log"
       # Localhost loop
       pass final on lo0 all
       # IPv6 ICMP
       pass final family inet6 proto ipv6-icmp all
       # IPv4 pings
       pass in family inet4 proto icmp icmp-type echo all
       # DHCP
       pass in family inet4 proto udp from any port bootps to any port 
bootpc
       pass in family inet6 proto udp from any to any port 
"dhcpv6-client"
       # SSH
       pass stateful in final family inet4 proto tcp to $ext_ip4 port ssh
       pass stateful in final family inet6 proto tcp to $ext_ip6 port ssh
       # Established outgoing connections
       pass stateful out final all
     }

There is no problem when npf is restarted with the command: 'service npf 
restart'

Now consider the same rules using a dedicated group.

     group "external" on wm0 {
       # SSH
       pass stateful in final family inet4 proto tcp to $ext_ip4 port ssh
       pass stateful in final family inet6 proto tcp to $ext_ip6 port ssh
     }

     group default {
       block all apply "log"
       # Localhost loop
       pass final on lo0 all
       # IPv6 ICMP
       pass final family inet6 proto ipv6-icmp all
       # IPv4 pings
       pass in family inet4 proto icmp icmp-type echo all
       # DHCP
       pass in family inet4 proto udp from any port bootps to any port 
bootpc
       pass in family inet6 proto udp from any to any port 
"dhcpv6-client"
       # Established outgoing connections
       pass stateful out final all
     }

Restart the nfp service closes the SSH connection.