I'm not sure whether this applies to debian-cd, debian-installer or
grub2; please move as appropriate.

I have an official Debian 7.8 dvd (disc #1) to hand, and I am loading it
in a virtualbox VM with efi enabled, thus the grub2 efi bootloader is
loaded. This displays as intended per the config at 800x600, however, if
you enter edit or command mode, this opens up in a significantly smaller
windows on top of the 800x600 menu window. Surely these should be shown
at the same size as the menu window.

Attaching an image to demonstrate the extent of the problem.

Checking edit mode this time also highlights a theme issue, as shown,
which I have just reported separately.

Of course I can only assume this problem still exists in the latest
d-i/grub2 builds to be used for Jessie since I have no practical means
of testing the latest version (I haven't used debian-cd before, I don't
really have the time to learn how and get things setup just now, and
live-build doesn't currently support EFI (I will shortly be working on
that)). I did browse through the changelogs/git-history for d-i,
debian-cd and grub2, and didn't notice anything suggesting this had been
fixed.