"org.postgresql.util.PSQLException: Cannot change transaction isolation" occurs at calling java.sql.Connection#setTransactionIsolation when enabling connection validation in JBoss EAP 6

Issue

When enabling connection validation (<check-valid-connection-sql>select 1</check-valid-connection-sql> or <valid-connection-checker class-name="org.jboss.jca.adapters.jdbc.extensions.postgres.PostgreSQLValidConnectionChecker"/>) in EAP 6 with PostgreSQL, the following "org.postgresql.util.PSQLException: Cannot change transaction isolation" was thrown at calling java.sql.Connection#setTransactionIsolation():

WARN  [org.jboss.jca.adapters.jdbc.local.LocalManagedConnectionFactory] (http-/127.0.0.1:8080-1) Error resetting transaction isolation : org.postgresql.util.PSQLException: Cannot change transaction isolation level in the middle of a transaction.
    at org.postgresql.jdbc2.AbstractJdbc2Connection.setTransactionIsolation(AbstractJdbc2Connection.java:929)
    at org.jboss.jca.adapters.jdbc.BaseWrapperManagedConnection.cleanup(BaseWrapperManagedConnection.java:357) [ironjacamar-jdbc-1.0.28.Final-redhat-1.jar:1.0.28.Final-redhat-1]
    at org.jboss.jca.core.connectionmanager.pool.mcp.SemaphoreArrayListManagedConnectionPool.returnConnection(SemaphoreArrayListManagedConnectionPool.java:479)
    at org.jboss.jca.core.connectionmanager.pool.AbstractPool.returnConnection(AbstractPool.java:586)
    at org.jboss.jca.core.connectionmanager.AbstractConnectionManager.returnManagedConnection(AbstractConnectionManager.java:452)
    at org.jboss.jca.core.connectionmanager.listener.NoTxConnectionListener.connectionClosed(NoTxConnectionListener.java:90)
    at org.jboss.jca.adapters.jdbc.BaseWrapperManagedConnection.closeHandle(BaseWrapperManagedConnection.java:584) [ironjacamar-jdbc-1.0.28.Final-redhat-1.jar:1.0.28.Final-redhat-1]
    at org.jboss.jca.adapters.jdbc.WrappedConnection.close(WrappedConnection.java:265) [ironjacamar-jdbc-1.0.28.Final-redhat-1.jar:1.0.28.Final-redhat-1]
    at  ...(snip)...