Brokers from 0.5 onward have an additional version=X key property in the MBean ObjectName. This was added in 0.5 to enable version tracking for the MBeans to accomodate compatibility checks where necessary after changes. In 0.6.0.0 a new version tracking system was put in place, using the new ServerInformation MBean. As such, the version key property in the ObjectName is no longer required.
Motivation for removing the key property is that for certain JMX operations that require knowing the exact ObjectName of the single remote MBean you wish to operate on, you must know the value of the version key, which is different on each type of MBean and also differs between releases. Whilst it is possible to easily Query the server for this information, the ability to first perform this query is not always available to the user (eg for non-bespoke server health checks) and as such they need to know the exact value in advance. Removing the now-unused version key from the ObjectName will remove this need in future broker releases.