Comment 8 for bug 1691158

"/boot != EFI partition. You should not be placing kernels in teh UEFI partition."
My root filesystem (sda10 in this case) contains the kernels, the sda5 EFI partition does not.
My sda10 partition does not contain a /boot/efi directory, so I created one and rebooted: sda5 is still mounted on /boot.
I then renamed that directory to /boot/EFI and rebooted: sda5 is still mounted on /boot.

Sda5 only contains Grub2 (and an unofficial PartedMagic spin) and is not really an EFI partition -- this flag is a leftover from an earlier experiment. So I removed that flag and rebooted once more: sda5 is still mounted on /boot ...

Perhaps superfluously I mention that I do not use Xubuntu's Grub/EFI setup, but PartedMagic's instead. The Grub stanza for Xubuntu reads:

menuentry '[10] Xubuntu 16.04.2 "Xenial Xerus"' {
  set root=(hd0,10)
  linux /boot/vmlinuz root=/dev/sda10 ro
  initrd /boot/initrd.gz
}
where /boot/vmlinuz is a symlink to ../vmlinuz and /boot/initrd.gz to ../initrd.img. The /vmlinuz and /initrd.img are symlinks back into /boot and are amended by the installing a new kernel version procedure. My /boot symlinks need no maintenance therefore.