ed maste pointed me here after he saw me post the following on twixter:
<<anybody in freebsd land know why in{6,}_pcbbind() doesn't propagate the interface FIB to the PCB (assuming that's still zero)? i've got a multi-homed dual-FIB server that's failing BCP38 and this seems pretty crusty.>>
to be clear, i can fix this and submit a patch, but won't if there are reasons why it was kept this way.
-- P Vixie