If you use pppd proxyarp and after you disconnect the peer you still see
that route comming back in routed,

Remove proxyarp and add to the end of /etc/rc.local:

arp -s <hostname> <ether_addr> pub

the <ether__addr> can be found with the command dmesg f.i. showing:
ae0 at nubus0: address 00:00:94:07:ee:b2, type MacCon Ethernet, 32k mem.
                       ^^^^^^^^^^^^^^^^^that's an ethernet address
~n