Along with being used in "content moved" responses, Location headers are often returned by RESTful APIs when content is successfully created via POST. Somewhere (though not in the proxy-handling method), abbot is apparently misunderstanding this Location header to be a "content moved" one, and re-POSTing to the new location. Then it's apparently appending the headers from the second response into the body of the first response, which is generally useless.
Along with being used in "content moved" responses, Location headers are often returned by RESTful APIs when content is successfully created via POST. Somewhere (though not in the proxy-handling method), abbot is apparently misunderstanding this Location header to be a "content moved" one, and re-POSTing to the new location. Then it's apparently appending the headers from the second response into the body of the first response, which is generally useless.