Network Change from 2.6.8 -> 2.6.15

I posted before and understand that you should not use a network
address as a default gateway or as a real entity address to use
(although Solaris' ip stack allows you to).

Network: I have a block of 8 ip's
Network Address: *.80
Subnet Mask: 255.255.255.248
Broadcast: *.87
Modem/Router: *.86

My setup is I have an adsl modem/router - this takes the *.86 address
but it seems internally (from reading the manual) that it also takes
the *.80 as the default gateway (Its a Westell 2400 that does private
lan nat'ing AND also wan routing simutaneously) - the manual says that
you should set the default gateway to this. I had a server running
2.6.8 and this was successfully setup to use a couple of the public ips
with the default gateway setup as *.80 (per Westell instructions). The
ip's are visible and outgoing services report the ip correctly (not the
gateway ip).

I upgraded to 2.6.15 and this setup has stopped working. Manually
setting up the network and it refuses to allow me to use the network
address as the default gateway or ping the *.80 address. (I could have
pinged the *.80 previously in 2.6.8).

Can any one help - or point me to a changelist say to why the move from
2.6.8 to 2.6.15 has changed the ip behaviour? Or is it time to change
modem/routers?