Comment 10 for bug 873551

I ran into this and believe I have found the root cause. In update-default-ispell, this logic is wrong:

  # Question is empty, but $class elements are installed. Two possibilities.
  if ( -x "/usr/bin/apt-extracttemplates" ){
    # apt-utils is installed. Other possibility is debconf database corruption.

Just because apt-utils is _installed_ doesn't mean the templates were parsed correctly. For example, if dpkg-preconfigure doesn't like the shell that d-i gives your late_command:

 Preconfiguring packages ...
 Unknown terminal: bterm
 Check the TERM environment variable.
 Also make sure that the terminal is defined in the terminfo database.
 Alternatively, set the TERMCAP environment variable to the desired termcap entry.
 debconf: whiptail output the above errors, giving up!

So update-default-ispell should not conditionalize on the existence of apt-extracttemplates to decide whether the database is corrupted or not. Regardless, update-default-ispell failing in the postinst should not be a fatal error.