resolution to duplicate issue from https://issues.apache.org/activemq/browse/AMQ-2980 - contention over active flag caused premature dispatch on reactivation such that there could be duplicates, fixing the contention sorts this, final piece of the puzzle, test now works as expected
activemq/trunk/activemq-core/src/main/java/org/apache/activemq/broker/region/DurableTopicSubscription.java