DBGvpp# set int ip address GigabitEthernet2/2/0 192.168.4.1/24
DBGvpp# set int state GigabitEthernet2/2/0 up
<ping vpp from 192.168.4.2>
DBGvpp# sh ip arp
Time FIB IP4 Flags Ethernet Interface
44.0926 0 192.168.4.2 00:50:56:b7:05:bb GigabitEthernet2/2/0
DBGvpp# ip route add 192.168.5.2/32 via 192.168.4.2
DBGvpp# sh ip fib
Table 0, fib_index 0, flow hash: src dst sport dport proto
Destination Packets Bytes Adjacency
192.168.4.0/24 0 0 weight 1, index 3
arp GigabitEthernet2/2/0 192.168.4.1/24
192.168.4.1/32 2 204 weight 1, index 4
local 192.168.4.1/24
192.168.4.2/32 0 0 weight 1, index 5
GigabitEthernet2/2/0
IP4: 00:50:56:b7:05:bc -> 00:50:56:b7:05:bb
192.168.5.2/32 0 0 weight 1, index 5
GigabitEthernet2/2/0
IP4: 00:50:56:b7:05:bc -> 00:50:56:b7:05:bb
DBGvpp# set int state GigabitEthernet2/2/0 down
DBGvpp# sh ip fib
Table 0, fib_index 0, flow hash: src dst sport dport proto
Destination Packets Bytes Adjacency
192.168.5.2/32 0 0 weight 1, index 5
unknown 65278 lookup fib index -258 shared -16843009 next_adj_with_signature -16843010

An immediate visit from my old girlfriend, Fifi... Well actually, 0xFEFE, the poisoned adjacency pattern. The adjacency share-count is botched. Any attempt to send traffic to 192.168.5.2 will end badly.

Need to check 16.06 for this issue.