Interesting. I have a trip KUL-SFO in P, fare basis PFA9OY4P. No warning whatsoever given until you get to the purchase page. (There is no warning in the screen where you select your flight)
Then you have to click on terms and conditions and further click on the highligthed fare rules until you get to

NOTE - -- HALF ROUNDTRIP FARE COMBINATION OF NON-REFUNDABLE / REFUNDABLE WITH A CANCELLATION PENALTY / FULLY REFUNDABLE - THE MOST RESTRICTIVE CANCELLATION PENALTY RULE APPLIES TO THE ENTIRE PRICING UNIT FOR WHOLLY UNUSED TICKET - -- NOTE - -- NON-REFUNDABLE APPLIES TO ADT/CHD/INF -- YR/YQ/6H/6I/6J/6K INTERNATIONAL SURCHARGE WILL NOT BE REFUNDED -- TAX/CHARGE - US/ZP/XF WILL NOT BE REFUNDED NON-REFUNDABLE ON NON-REFUNDABLE FARE TICKETS -- CHANGES/CANCELLATIONS TICKET IS NON-REFUNDABLE. CHANGES NOT PERMITTED.

This is the only warning you get and it is buried pretty deep. It is unlikely that many people will do a deep dive into Terms and Conditions and then click again on fare rules (which does not open automatically).

Safe travels