Server 2012 DHCP Server Failover - Hot Standby

Hi There
I'm running two Windows Server 2012 R2 servers, they are configured in a Hot Standby mode for DHCP Failover. ServerA, is the local server at the site and is configured to Failover to ServerB. But I'm having an issue where after the state of ServerA changes
from Normal to Communication_Int and then back from Communication_Int to Normal that it's no longer leasing any IP address to my Windows 7 clients until you restart the DHCP service on ServerA. I've replicated this in my lab environment as well.
1. Disable Network Adapter on ServerA or disconnect Network - State changes from Normal to Communication_Int. ServerA and ServerB loses contact.
2. Enable Network Adapter on ServerA or reconnect Network - State changes from Communication_Int to Normal. ServerA and ServerB re-establishes contact.
3. Connect new computer to LAN, or release IP on client computer, and then try to obtain an IP address\renew.
4. Client computers time out trying to communicate with DHCP server, but as soon as you Restart the DHCP service on ServerA the client machines obtain an IP address.
Has anyone else experienced this? If so is there a fix/workaround for this?
Thanks

Hi
Sorry for only replying now.....
Disabled firewall on ServerA, ServerB and client machine. Issue still occurring.....

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