ARP requests for IP not on the local network

[GlenK]

I have an IPsec tunnel between various private networks. Traffic between 192.168.20.247 and 192.168.120.243 isn't going through. Running tcpdump on my router, I'm seeing this:
13:40:27.304223 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.20.247 tell 192.168.120.243, length 46

tcpdump on the CentOS machine I'm having trouble pinging:
192.168.20.247 > 192.168.120.243: ICMP echo request, id 5700, seq 1, length 64
15:55:28.085278 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 192.168.20.247 tell 192.168.120.243, length 28

So it's like this thing has a /16 netmask or something. Except it's /24. And except it's not like that at all:
-bash-4.2# ping 192.168.20.247
PING 192.168.20.247 (192.168.20.247) 56(84) bytes of data.
From 192.168.120.243 icmp_seq=1 Destination Host Unreachable

-bash-4.2# ping 192.168.20.1
PING 192.168.20.1 (192.168.20.1) 56(84) bytes of data.
64 bytes from 192.168.20.1: icmp_seq=1 ttl=63 time=60.0 ms
64 bytes from 192.168.20.1: icmp_seq=2 ttl=63 time=60.2 ms

I filed a bug report about it, because it sure seems like a bug to me, but maybe someone could enlighten me as to what if anything I'm doing wrong.

Thanks in advance,
Glen