Well the bootloader is not always as critical as the kernel and oe been the same because the image in external will use the bootloader and drivers from the image in the flash, but if the drivers or something in the bootloader does not match the kernel then you have errors in external images.
Best thing to do is alway have latest image in flash and use latest images in multiboot.
There are so many variables these days it can make you loose your mind at times.
Ferret