Why does JBoss EAP create more than 2 * max-pool-size connections to an IBM WebSphere MQ server?

Issue

• Why does JBoss EAP create more than 2 * max-pool-size connections to an IBM MQ queue manager?

• When configuring the IBM WebSphere MQ resource adapter as follows, EAP should use 5 connections, but the queue manager shows over 10 connections.

   <transaction-support>XATransaction</transaction-support>
   ...
   <connection-definition class-name="com.ibm.mq.connector.outbound.ManagedConnectionFactoryImpl" jndi-name="java:jboss/mqm" enabled="true" tracking="false" use-java-context="true" pool-name="java:jboss/mq/xa/mq-cd">
      ...
      <xa-pool>
          <min-pool-size>5</min-pool-size>
          <initial-pool-size>5</initial-pool-size>
          <max-pool-size>5</max-pool-size>
          <prefill>true</prefill>
      </xa-pool>
      ...
  </connection-definition>
  

• Checking the JBoss EAP resource adapter statistics in the CLI (/subsystem=resource-adapters/resource-adapter=<RAR>/connection-definitions=<CONNECTION DEFINITION>/statistics=pool:read-resource(include-runtime=true)) shows max-pool-size available and active, but IBM MQ shows twice, or more connections to the queue manager.