the Active MQ load balance

We install activemq on 2 Linux vm servers.
we have 1 NFS shared folder that running on different machine.

When we disable the network from the master server, server 2 become master and all fine, but when we enable again the network , both server 1 and server two become master ( we can enter to admin page, topic message can be send to both)
This is critical issue since client can be connected to any one and will miss msges.