I'm just as baffled with your reply as you are with my post.
You say "It booted, it installed and just worked". It sounds like you have only one distro installed and therefore never needed the UEFI Boot Options. I only ever had Ubuntu, the first in boot sequence, start by itself immediatly after pressing the power-on switch.
Although there is a single specification of UEFI, there are different implementations. The version number of mine, from Dell, is 1.2.0.
When multibooting, you must somehow have a menu of installed systems from which you then select which one to boot. Just like in Grub2, when you press the power-on switch, 2 options appear in the lower right corner: Setup and Boot Options, selected by function keys. On my computer F2 displays the UEFI configuration and allows modification of boot order, among other things. F12 displays the list of installed distros, in the boot order you selected in Setup(F2). Just to test things out, I installed xubuntu, debian/xfce, and solydx.
Refind is another boot manager, just as Grub is a boot manager, only it has some features that Grub does not have and actually utilizes Grub. Also, I don't think that there is an MBR on a GPT system.
There is also an earlier version of Refind in the Solydxk repos.
I had hoped that Refind would pick up the slack from the EUFI and display everything in the proper resolution. But it didn't, so I deleted it.
(1) No, Of course I am not "starting the ISO with the F12 menu". I am displaying the UEFI Boot Options and selecting the installation of that particular solydx iso.
(2) I installed 3 systems: xubuntu, debian/xfce, and solydx. Xubuntu is the only system that always boots with the correct resolution.
(3) I can select a system to boot by:
(a) pressing F12 to display the UEFI Boot Options and then select an option from a list of distros.
This works for each of the 3 distros correctly.
(b) Select Log Out in a running distro and then select from that Log Out window: Restart.
This only works for the first distro in the boot list when that distro is ubuntu.
Debian or Solydx display with the wrong resolution.
This is what "previous running system exits with Restart" means.
It's the same Restart that you get from Log Out with Grub.
Therefore, I believe that our miscommunication revolves around the fact that I have a multiboot system and you have a single boot system, and have never displayed the UEFI Setup or Boot Options. I would really love for you to install a second distro on one of your UEFI/GPT boxes. Preferably Debian.
I would also like to know just how screwed I am with a UEFI version of 1.2.0. I understand that currently there is a 2. version.