it probably has something to do with the actual business arrangement of this route...

yes, the particular flights you are looking at might have CX flight numbers and are operated by CX...however, services on this route HKG-HAN (and HKG-SGN as well) are in fact what they called "joint venture"...

i don't know the details, but i guess it's probably like two airlines (CX + vietnam airlines) operating as one airline and selling seats together...vs in the case of code-share one airline is actually buying seats from the operating airline to re-sell to their own passengers...again, i don't know the details, but maybe it's this "joint venture" that makes things complicated...that the flights are not officially operated by CX alone, but by CX and vietname airlines together...

i believe this "joint venture" arrangement is what the vietnamese government requested ?