I suspect the problem was your USB drive already had a MBR.
Well, I would not know what the thinking was then as UEFI booting is independent of the USB stick having an MSDOS or a GPT disk label -- as my manual copy of the EFI directory showed.
Anyway, I repeated my test with an GPT USB stick: problem persists.
I then repeated my test with an ext4 partition on the GPT USB disk: problem persists.
I then burnt the Porteus_CINNAMON-v3.2.2-x86-64.iso to a CD and with that repeated my test to the fat32 partition on a GPT USB disk: problem persists.
In the Cinnamon test the Installer window closes, whereas with the Mate ISO things seem to be cut short -- see this https://drive.google.com/file/d/0B0gP2v ... sp=sharing
screenshot. But tracing the Cinnamon test also shows the cutting short.
So, is the super-floppy format the discerning factor here? For as far as I am aware there is nothing in the documentation hinting at that.
I added researching things to my todo list. Do not hold your breath though.