Every connection pool I know wraps returned connections in a transparent proxy and intercepts close(). When client code calls close(), this invocation is actually handled by the pool and instead of physically closing the connection it puts it back into the pool.

If you don't call close(), pool will think you are still using the connection and never reuse it - this is known as connection leak. Simply put - IMHO this works as desired and is correct. Are you actually experiencing any issues with DB appender?