What causes 'org.apache.tomcat.jdbc.pool.ConnectionPool.abandon Connection has been abandoned' in JBoss Web Server?

Issue

• Encountering the WARNING below in JWS logs

  ... WARNING [Tomcat JDBC Pool Cleaner[...]] org.apache.tomcat.jdbc.pool.ConnectionPool.abandon Connection has been abandoned PooledConnection[...]:java.lang.Exception
          at org.apache.tomcat.jdbc.pool.ConnectionPool.getThreadDump(ConnectionPool.java:1163)
          at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:816)
          at org.apache.tomcat.jdbc.pool.ConnectionPool.borrowConnection(ConnectionPool.java:660)
          at org.apache.tomcat.jdbc.pool.ConnectionPool.getConnection(ConnectionPool.java:198)
          at org.apache.tomcat.jdbc.pool.DataSourceProxy.getConnection(DataSourceProxy.java:132)
          ...
          at org.myco.MyClass.someMethod(...)
  

• System has configured removeAbandoned*/logAbandoned properties