this is not related to the satellite.
If your uplink antenna (feed) is really linear polarized then you should not see a difference in the downlink signal strength when turning your feed.
However make sure that you are not turing the uplink feed and downlink feed at the same time as this will influence the downlink strength.
It might be better for such a test to use the Web-SDR to watch the downlink signal when optimizing the uplink antenna (feed).
The QO-100 transponder has not changed.