WTF LMDE?

I've been searching for half an hour why an update-grub doesn't add my parameters from /etc/default/grub to the kernel command line...

> tail -6 /etc/default/grub.d/50_lmde.cfg
# grub-pc's postinst has some unwanted conffile management which removes
# /etc/default/grub, thus removing "quiet splash" from grub.
# Setting it here ensures we continue to have a splash, whether or not
# /etc/default/grub is present.

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"