Example on macOS (current)
It's an 8G stick, but there are three partitions totally less than
20M. Formatting any of the partitions will get me no where; and I
can't even add partitions in the partition UI (oops). What I have to
do is click on the stick itself, not any of its volumes, click Erase,
and give it a new partition map. Plus it defaults to legacy Apple
Partition Map because we're using a fragment of APM to trick certain
Mac firmwares into booting in EFI mode from USB sticks.
What's going on is the ISO 9660 image is not on a partition (it's not
meant to be combined with partitioning of any kind). It's basically a
hidden payload. The MBR map is there to boot BIOS computers, APM for
some Macs, and GPT for UEFI computers.
The other thing is ISO 9660 since it's an optical format specifies
2048 byte sectors and I guess this causes confusion elsewhere (I'm
handwaving on this one because I can't remember exactly, maybe mbriza
will chime in) since USB sticks are 512 byte sectors; and they end up
appearing much larger than they really are or something?
Meanwhile in GNOME, it sees this same stick rather differently because
it ignores the APM and GPT, preferring to honor the MBR.
I don't know off hand what sees all three partition maps and knows to
wipe all three signatures, so there could even be really weird latent
after effects even if something successfully reformats the stick.