In my project, it appears that %contentResponse is always empty. If I instead use %fullResponse, I do see the headers for the response. With a pattern of "%date %requestURL\n%fullResponse\n-----" I get the following for a request:

07/09/2014:19:09:38 -0600 GET <path> HTTP/1.1
HTTP/1.1 200 OK
Date: Mon, 8 Sep 2014 01:09:38 GMT
Content-Length: 822
Expires: Mon, 8 Sep 2014 01:09:38 GMT
X-Lift-Version: 2.5.1
Content-Type: text/javascript; charset=utf-8
Cache-Control: no-cache, private, no-store
Pragma: no-cache

I snipped out the path, but otherwise didn't edit the output. You can see the Content-Length is 822 but there's no content in the output. I tried using versions 1.0.13 and 1.1.2 of logback-classic and logback-access.

Please let me know what additional information would be helpful.