Package app-emulation/xen installs a config file to (e.g.) /boot/xen-4.12.1.config. Later, when running grub-mkconfig, this file is interpreted as a multiboot image and incorrectly added as a separate menuentry, which does not work.
Steps to Reproduce:
1.install sys-boot/grub and app-emulation/xen
There is a menuentry in the output produced by grub-mkconfig, pertaining to "/boot/xen-4.12.1.config".
The menuentry should not be there; the "/boot/xen-4.12.1.config" config file should be ignored when creating boot menu entries.