"arch/x86_64/airootfs.sfs is missing" problem with non-UEFI VirtualBox + 6.0.2 ISO + archiso non-UEFI grub boot examples

Boot fails with custom grub.cfg and iso loop mount in VBox 6.0.4 r128413 (Qt5.7.1) on Intel i5-3360M.

The error message is "losetup: /run/archiso/bootmnt/arch/x86_64/airootfs.sfs: falied to set up loop device: No such file or directory".

The quick-ugly workaround is to modify the ISO by copying sysresccd/x86_64 to arch/x86_64/.

Grub config's releavant part (hopefully not missing anything):

set srcd='srcd602p1.iso'
set gfxpayload=1024x768x16, 1024x768
probe -u $root --set=rootuuid
set imgdevpath="/dev/disk/by-uuid/$rootuuid"
insmod search_fs_uuid
search --no-floppy --set=isopart --fs-uuid $rootuuid

menuentry "Test1" {
        loopback loop ($isopart)/$srcd
        probe -l loop --set=isolabel

        linux (loop)/sysresccd/boot/x86_64/vmlinuz img_dev=$imgdevpath img_loop=$srcd earlymodules=loop
        initrd (loop)/sysresccd/boot/intel_ucode.img (loop)/sysresccd/boot/amd_ucode.img (loop)/sysresccd/boot/x86_64/sysresccd.img
}