Just wondered if this has been noted before, is it common, anyone know why?

If I make a reservation, say weekly, and enter my CDP code and a PC code, I get X rate.

If I try and make the same reservation, using the same CDP code and PC code, but click the box indicating I may want to use my Gold points, I get XX rate, which is higher (before applying my Gold points).

I've tried it on a number of different potential reservations.-

Has it always been the case or is it just being impacted by the codes i happen to be trying?