this isn't a fix, but a workaround that is fairly easy: dd boot.img /dev/sdX, mount it, cd it.
mkdir -p efi/boot grub-mkimage -o bootx64.efi -p /efi/boot -O x86_64-efi \ fat iso9660 part_gpt part_msdos \ normal boot linux configfile loopback chain \ efifwsetup efi_gop efi_uga \ ls search search_label search_fs_uuid search_fs_file \ gfxterm gfxterm_background gfxterm_menu test all_video loadenv \ exfat ext2 ntfs btrfs hfsplus udf create grub.cfg