I put the Qubes-R4.0.4 ISO on a memory card (it boots). However when I inspect the partitions, I'm quite surprised:
# fdisk -l /dev/sdg
Disk /dev/sdg: 7.4 GiB, 7969177600 bytes, 15564800 sectors
Disk model: STORAGE DEVICE
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x501be065
Device Boot Start End Sectors Size Id Type
/dev/sdg1 * 0 10156031 10156032 4.9G 0 Empty
/dev/sdg2 1028 61375 60348 29.5M ef EFI (FAT-12/16/32)
So the EFI partition is not marked bootable (active), and it overlaps the other partition?
I wouldn't be surprised if some BIOS complained...
I see other images also don't mark the EFI as bootable, but they don't use overlapping partitions.