S7 in DME also keeps the small portion,but keeps the big portion almost everywhere else. In DME they leave the "large" part for you in case they have to offload the whole plane and "reboard",it makes it easier for them,as they can just scan the barcode (which is located on the "large part") again when reboarding,rather than keying in the B/N.

CX in HKG and BA in LHR normally don't detach the BP at all.