This is the type of thing that can happen mixing and matching MP4,1 and MP5,1 EFI components inside the BootROM, but I'm really not sure if it's caused by the cross-flashing process and could be an Apple oversight/bug.Off topic: @tsialex, regarding the original FirmwareFeatures, there is a mismatch of one bit (bit 14 = FW_FEATURE_SUPPORTS_HIGH_SPEED_USB) between the values in the SMBIOS and the NVRAM. This seems like an Apple bug, but I wonder if it could not actually be an artifact of cross flashing. Do you have any insights on this?
I'll investigate between the different model years and get back to you after the weekend.