The reason is simple. If you insert a card when the board boots the H3 will always search for a bootloader there. If you insert the card later it won't be recognized (which might be able to be fixed by playing around with /proc/driver/sunxi-mmc.x/insert).   So to boot with inserted SD card the bootloader has to remain there and point to the rootfs on the eMMC (the numbering of devices will then also change!). This can be done by using our nand-sata-install.sh script and then not wiping out the