Oneworld instituted a policy last year where its members airlines would not through checks bags if on separate tickets.
Seems that this policy has started to crack, however. Qatar made an announcement recently (read more here) that they would roll back this function and Cathay Pacific now does it officially again as well (email was sent to program members today).
Here’s the Cathay’s web page for this change (access here):
Since the beginning of the year, as a courtesy, Cathay Pacific and Cathay Dragon will through-check you and your baggage to your final destination if you are travelling on separate tickets. This means there is no need for you to collect your baggage and check it in again with your connecting carrier, thus allowing you to enjoy a smoother travel connection with our airline partners. You will still be subject to local passenger security or customs policies.
However, through-check may not be possible if your travel begins with an airline that does not provide a separate ticket through-check service. Please contact your originating airline directly for more details.
Passengers with connecting itineraries booked on a single ticket or connecting between Cathay Pacific Group-operated flights will be through-checked to their final destination.
Please visit our travel information page for more details.
Cathay’s FAQ clarifies “Partners”:
1. What is Cathay Pacific and Cathay Dragon’s separate ticket through-check in policy?
As a courtesy, Cathay Pacific and Cathay Dragon will through-check you and your bags to your final destination if you are travelling on separate tickets involving connections with our interline partners. However through-check may not be possible on their return journey if your travel begins with an airline that does not to provide separate ticket through-check service.
Passengers holding connecting itineraries booked on a single ticket or connecting between Cathay Pacific Group operated flights will be through-checked to their final destination regardless.
2. What happens on the return journey?
If you travel begins with another airline, you will be subject to their separate ticket through-check policy. Please contact them directly for details.
3. If a disruption occurs, what is Cathay Pacific and Cathay Dragon’s obligation?
Cathay Pacific and Cathay Dragon are obligated to transport you to your destination as stated in your itinerary with us. If you have a connecting flight ticketed within the same itinerary, please approach our airport staff for assistance and we will do our utmost to make arrangements for an alternative flight to your final destination.
If you purchased a separate ticket for your onward flight with another airline, your baggage has been tagged to your final destination. However, for flight arrangements to your final destination, please approach the onward carrier for assistance upon arrival.
Refusing to through check bags on separate tickets has never been anything else than revenue protection for the airlines. They would prefer that you wouldn’t shop around and buy one ticket from your origin to destination.
Note that this change doesn’t affect how airlines deal with irregular operations if flying on separate tickets. I would leave plenty of time between flights just in case.