The 1.1.4 release adds the following check on the xmlHttpRequest object when dataType is 'xml':

if ( xml && data.documentElement.tagName == "parsererror" )
  throw "parsererror";

This raises an error when malformed xml is sent to the browser, which is desirable behavior, but it also raises an error when the server responds with an HTTP HEAD response (which has a blank body) to indicate success.

This change therefore breaks compatibility with existing apis that use HTTP HEAD responses to indicate success.

I've added logic so that a blank response body can pass through successfully:

if ( xml && r.responseText.match(/\\S/) && data.documentElement.tagName == "parsererror" )
  throw "parsererror";