[ubuntu] bridge interface, kvm client not getting DHCP offer

Hi,

I'm playing around with some KVM setup using ubuntu 14.04.5. I've created a bridge with just one physical interface attached to it.
When I bring up a cirros kvm image attach the the bridge, it tries to get a DHCP address and an reply is entering my ethernet interface.

~$ sudo tcpdump -i eth1 | grep -i dhcp
15:28:15.708218 IP 0.0.0.0.bootpc > 255.255.255.255.bootps: BOOTP/DHCP, Request from 52:54:00:cf:dd:39 (oui Unknown), length 290
15:28:18.122965 IP 10.0.0.2.bootps > 10.0.0.3.bootpc: BOOTP/DHCP, Reply, length 300

But the reply never makes it to the cirros client. When we filter the vnet0, only the request is seen, no reply.
~$ sudo tcpdump -i vnet0 | grep -i dhcp
15:29:20.642181 IP 0.0.0.0.bootpc > 255.255.255.255.bootps: BOOTP/DHCP, Request from 52:54:00:cf:dd:39 (oui Unknown), length 290

But when we attach a static IP to the cirros eth0 interface, we can ping the DHCP server.

Is there some filtering going on somewhere that's dropping the DHCP offer?