Comment 5 for bug 22306

Yes, I did understand your main complaint. debconf's Readline frontend is
supposed to invoke readline in such a way that the default value of the variable
is set as the initial input string, so that you can just press Enter and get the
default. Since it is not working for you, there must be a bug, and therefore I
was attempting to diagnose this bug by finding out whether xserver-xorg was
buggy in claiming that proper defaults would be set and then failing to do so,
or whether debconf was failing to drive readline properly, or whether in fact
the Teletype frontend was in use (which is a fallback from Readline, so you
could have ended up using it even after seeing the messages you quoted in your
report). It could have been any of these, and there's no point in me chasing
bugs in one when another situation applies.

From the DEBCONF_DEBUG=developer log, though, it looks like xserver-xorg is
behaving correctly, and you're definitely using the Readline frontend, so
something's up with the default-handling code in debconf's Readline frontend.
Could you please show me the output of "dpkg -l 'libterm-readline-*-perl'", so
that I can get the right readline implementation installed and thereby replicate
this? Thanks.