I had this happen to me going SLC-IAH-LGW. The SLC-IAH was a DL codeshare and the DL agent rebooked me in Y SLC-CVG-. When I complained, he was such a jerk and told me it was "take it or leave it" and that my behavior indicated I didn't want to get on the plane, when I asked to speak with his supervisor he told me none would be available until after the SLC-CVG flight departed.
just another day with DL service