In the 15OCT92 version of AIPS the following CHANGE.DOC entry
appears:
 7004.  June 4, 1992         UVLIN                      Tim C.
        The phase shift option was really screwed up: it shifted the
        correct amount before fitting but then only shifted back
        by 1/(2 pi) of the correct amount afterwards.
        Moved nowhere.
This would seem to match your experience.
Eric