Message count in queue.JbpmTimerQueue continue to build up in SOA-P 5.3

Issue

Our application is built on SOA platform and jBPM 3. We have JMS scheduler configured for the jBPM timer.

The application is functional (timer can be set and expired as expected) except the message count in queue.JbpmTimerQueue continues to build up.

My question is why this message is not been removed after it's been consumed? With the number going up, is there any performance issue that comes with? Or this is just the way it should be, we just need to find a way to purge it from the table?

For instance, the record number in the JBM_MSG table is 110812, and the record number in the JBPM_JOB table is 28459.