I've had this happen in HKG as a Emerald passenger, but not too often. Usually I spend some extra time in the lounge and wait until they are still boarding Y and there is no F/J line - they may very well be doing it more often.

Seriously, even if you're at the gate, what's the rush to wait in line? running out of overhead space is rarely an issue on the widebodies? Do people just love waiting in line?