Regarding UEFI vs Legacy mode. If I understand it correctly it happened in UEFI and not Legacy mode. I am not sure but I think my Lenovo Yoga 2 doesn't have Legacy "old school" BIOS and it only has UEFI. It has "BIOS backport" feature but I don't know if that's what you mean. In either case BIOS backport was disable by default on the laptop.
Regarding UEFI vs Legacy mode. If I understand it correctly it happened in UEFI and not Legacy mode. I am not sure but I think my Lenovo Yoga 2 doesn't have Legacy "old school" BIOS and it only has UEFI. It has "BIOS backport" feature but I don't know if that's what you mean. In either case BIOS backport was disable by default on the laptop.