Actually, the buggy file (/etc/grub.d/20_linux_xen) belongs to the
grub2
package, so the bug is assigned to a wrong package.
Not that it matters, but I'd originally assigned it to grub. It was ignored there as
well.
I switched it to Xen after I was told in #irc to do so.
Too much pushing rocks uphill for my taste. Building my own.