Disconnect of primary OpenLDAP freezes network

I am running two Ubuntu 12.04 LTS systems, one physical one virtual, configured as primary/secondary.

Physical - Primary LDAP, Secondary DNS/DHCP

Virtual - Secondary LDAP, Primary DNS/DHCP

I've noticed that if the physical server loses it's network connection clients on the network freeze (majority linux). The clients ARE ssh'd in to network servers and mounting NFS exports but shouldn't the secondary system take over or have I missed something.

Any ideas on what items I should look at or which configuration information would be helpful in diagnosing this?