Default route from DSL modem ignored

Hi.  I am attempting to use an edgerouter POE-5 on a DSL modem (Comtrend CT-5072T).  The modem is configured in one of its "pass-thru" modes, whereby a client connected by ethernet will receive the public address by DHCP.  This all works fine with stock dhclient and dhcpcd on a generic Linux machine.

When an edgerouter is substituted, the edgerouter picks up an interface address, but fails to configure the default route.  Curiously, the modem provides a default route identical to the leased address.  Here is the lease:

sh-4.2# cat /var/run/dhclient_eth0.leases 
lease {
  interface "eth0";
  fixed-address X.X.86.227;
  option subnet-mask 255.255.255.0;
  option dhcp-lease-time 86400;
  option routers X.X.86.227;
  option dhcp-message-type 5;
  option dhcp-server-identifier 192.168.1.1;
  option domain-name-servers X.X.X.243,X.X.X.243;
  renew 4 2015/01/01 10:29:34;
  rebind 4 2015/01/01 21:29:22;
  expire 5 2015/01/02 00:29:22;
}

The default route provided with the lease appears to be ignored.  Logs do not indicate a reason.

To work around this, I configured a static route as follows:

# show protocols static
 interface-route 0.0.0.0/0 {
     next-hop-interface eth0 {
         description "Work around ppp ip extension same nexthop as if addr"
         distance 1
     }
 }

This static route is inserted into the system routing table when added.  However, it disappears whenever the DHCP lease on the eth0 interface is renewed.  Is this in itself a bug?  How can I force a static route to always be in the routing table?

Here is my interface configuration:

# show interfaces ethernet eth0 
 address dhcp
 description Internet
 dhcp-options {
     name-server no-update
 }
 duplex auto
 firewall {
     in {
         name WAN_IN
     }
     local {
         name WAN_LOCAL
     }
 }
 poe {
     output off
 }
 speed auto

Thanks.

Jacob