My experience is doubling dipping is an aberation. I am told at the check-in desk that I can use one card or the other. I always book under the GoldCrownClub card and number, but in Canada and the US have my miles credited to CP (though I have now had them credited to AA). Through the rest of the world you can only credit points to the GoldCrownClub, so it is useful to keep an active account open. (You must have one stay per year to keep your account. I have talked to them many times about this requirement, particularly for those who have points credited to airline partners, but to no avail. Even with 10 stays credited to CP or AA, I still have to post one to GCC. But with their vast range of mid-price, quite acceptable hotel affiliates around Europe, this is not difficult.)

I also find posting to airlines is a problem, and can take forever. I now just copy my bill and send/fax a copy to the CP or AA office for verification/credit.