An LNB can see some amount of signal from transponders of both opposing polarities, even without any change in the LNB's polarity adjustment. Attenuation of adjacent signals by polarization can be very effective, but is always less than absolute. The greater the strength of the incoming signals, the more this becomes evident.
If the LNB is aligned to a polarity position between what would be optimal for one polarity or the other, the difference between the signals is diminished.
If you try rotating the Norsat for optimal performance on one polarity. You should see a very noticeable degradation in performance on transponders of the opposite polarity.