Mirrored queue unwanted persistence

Hello Activemq community,

we are working with activemq 5.6.0 and recently decided that we want to use
mirrored queues and have been trying them out.
According to this: http://activemq.apache.org/mirrored-queues.html mirrored
queues behaves as topics. As such messages send to the mirrored queue should
not be persisted if there are no subscribers for it.
We are having an application running right now that sends messages via a
queue on which a mirrored queue is active. This mirrored queue seems to
persist messages send to it, even in the absence of subscribers.

"2014-06-18 14:36:40,167 | INFO |
Usage(default:memory:topic://Mirror.xactive.alarm.45678:memory)
percentUsage=100%, usage=1049824, limit=1048576,
percentUsageMinDelta=1%;Parent:Usage(default:memory) percentUsage=4%,
usage=3159988, limit=67108864, percentUsageMinDelta=1%, Usage Manager memory
limit reached for topic://Mirror.xactive.alarm.45678. Producers will be
throttled to the rate at which messages are removed from this destination to
prevent flooding it. See
http://activemq.apache.org/producer-flow-control.html for more info |
org.apache.activemq.broker.region.Topic | ActiveMQ Transport:
tcp:///192.168.100.15:62727"

This causes the producer that sends to the original queue
"xactive.alarm.45678" to hold.

Is there some configuration that is needed to prevent this behaviour? We
would have expected the messages that land Mirror.xactive.alarm.45678 to be
deleted in the absence of any subscribers.

Any and all clarification would be most welcome.