Unknown flows in dump-layer

I've noticed that opteadm dump-layer will sometimes show "unknown" flows that seems to just all-zeros:

$ pfexec opteadm dump-layer -p opte_nexus0 firewall
Layer firewall
======================================================================
Inbound Flows
----------------------------------------------------------------------
PROTO  SRC IP           SPORT  DST IP           DPORT  HITS     ACTION                
TCP    192.168.1.2      63016  10.0.0.5         443    0        no-op                 
TCP    192.168.1.2      63018  10.0.0.5         80     0        no-op                 
TCP    192.168.3.2      63016  10.0.0.5         443    1        no-op                 
Unknown 0.0.0.0          0      0.0.0.0          0      0        no-op                 

Outbound Flows
----------------------------------------------------------------------
PROTO  SRC IP           SPORT  DST IP           DPORT  HITS     ACTION                
TCP    10.0.0.5         80     192.168.1.2      63018  1        no-op                 
TCP    10.0.0.5         443    192.168.1.2      63016  2        no-op                 
TCP    10.0.0.5         443    192.168.3.2      63016  0        no-op                 
Unknown 0.0.0.0          0      0.0.0.0          0      0        no-op                 

Inbound Rules
----------------------------------------------------------------------
ID     PRI    HITS   PREDICATES                             ACTION            
0      100    17     inner.ulp.dst=80,443                   "Stateful Allow"
1      65534  75     inner.ether.ether_type=ARP             "Stateful Allow"
DEF    --     1021   --                                     "deny"

Outbound Rules
----------------------------------------------------------------------
ID     PRI    HITS   PREDICATES                             ACTION            
DEF    --     0      --                                     "stateful allow"

Unsure if that's expected but figured I'd just open an issue so I don't forget to investigate more.

Start by reproducing the pfexec opteadm dump-layer -p opte_nexus0 firewall output and trace the dump-layer flow display and decoding path. Determine why all-zero flows are reported as Unknown, whether they are expected, and what observable behavior should count as resolved.