Some requests to CQ produce the following error message in your instance log file:
21.08.2006 09:59:55 *ERROR* delivery: popOutput: Problem closing the output: Broke
This issue occurs when the request was interrupted from the client side. The browser closed the socket before the response was completely sent. It can happen when you click the Stop button on your browser for example, or if the client decides to deliver the request from cache. This behavior is expected.