Adjust timestamp-difference to address DST boundary

With the current implementation of local-time the timestamp-duration+ and timestamp-duration- operations will adjust the result when it crosses a DST boundary.  However timestamp-difference does not.  This results in the following, which feels inconsistent to me.

(setf test-diff (start end) 
(ltd::timestamp-duration+

(let ((start @2014-11-02T00:00:00.000000-05:00)
      (end @2014-11-03T00:00:00.000000-06:00))
   (ltd::timestamp-duration+
       start (ltd::timestamp-difference end start)))

=> @2014-11-03T01:00:00.000000-06:00