Problems to change to tty from graphical environment

Hi all:

I want to ask you about a problem with tty in Debian GNU/Hurd.

A few weeks ago, I got install Debian GNU/Hurd 2017 in a real PC, with
spanish layout and Xfce as DE.

I start Xfce using startx from the tty, and It runs well, but once it has
started, I can't return to tty.

From any tty, I can change to another using the keycomb Alt+fX, but when I
try this from any graphical environment (not only Xfce) the keycomb don't
work.
It don't shows any error, simply It doesn't do anything.

I also tried with Ctrl+Alt+fX, as I do in GNU/Linux, but unsuccessfull.

Do you know how can I solve this?

Thanks