My reply got eaten so I'll try again.
The BIOS is an UEFI BIOS but I have transplanted a 2TB MBR disk to it and it works fine so perhaps the BIOS is doing some sort of auto-detection.
I created a USB pen version of gparted using LinuxLive USB Creator and it worked fine. I've just tracked down a 2013-08-01 iso version of Parted Magic and put that on a USB pen with LinuxLive and it has the same problem so I assume it is a Parted Magic issue.
Since all I want for the moment is a partition manager, text editor and file manager, it looks like the gparted iso will do the job. I just liked having all the other utilities on one distro