Comment # 1 on bug 907672 from Neil Rickert

A comment on your attempt to boot Windows:

Try using a variable name other than "$prefix".  The name "prefix" seems to
have a special meaning to grub2-efi, and I think that may be what is causing
the Windows problem.  Grub2-efi seems to wants use $prefix to find its own
files (loadable grub-modules, for example).

Your other problems appear to be due to an inadequate UEFI implementation by
your firmware.