Recently a new message was added to d-i:

 This machine's firmware has started the installer in UEFI mode but
 it looks like there may be existing operating systems already
 installed using "BIOS compatibility mode". If you
 continue to install Debian in UEFI mode, it might be difficult to
 reboot the machine into any BIOS-mode operating systems later.

Please consider replacing "Debian" with `lsb_release -si` or similar
so that people installing other distros based on debian don't get a
message about a different operating system than the one they are
installing.

Quoting Phillip Susi (psusi@ubuntu.com):

Doh. That one escaped my attention when this message was added.

We usually avoid hardcoding "Debian" and this is probably one of the
very rare cases where we failed. The message was added in a bit of a
hurry recently and that failed to be catched by the review....:-(

Sadly, I'd prefer us not to change  this now.....as it will require
Yet Another Round of translation updates....which takes weeks to
achieve.

I'd prefer something like "If you continue to install in UEFI
mode, it might be difficult to reboot the machine into any BIOS-mode
operating systems later" and avoid "the distro" or anything like
that. The output of "lsb_release -si" is likely to not work.

But even just dropping "Debian" does not guarantee we can easily fix
translations as it is likely that, for some languages, dropping the
distro name wouldn't be enough.

ACK. Sorry, my fault guys. :-(

Works for me, yeah.