I have a running ProxmoxVE 3.1 cluster which is up-to-date and can reach all destinations.
I have installed the default debian-7 template to a node, with bridged network via a veth interface. The guest gets its IP via DHCP on a separate router (which I tested), but it can only reach the node it is residing on. I have run tcpdump on the node for the veth of that guest and I see a lot of ARP traffic that goes unanswered.
There is no firewall running.
I have not been able to diagnose this properly, but when I installed a cluster using real hardware (as opposed to virtual machines) everything worked properly.