kubuntu-devel-release-upgrade crashes when terminal input is required

When using Kubuntu 13.10, I attempted to upgrade to Kubuntu 14.04 using `kubuntu-devel-release-upgrade` as recommended [1].

The GUI progressed through "Preparing to upgrade", "Setting new software channels" and "Getting new packages", and then stalled on "Installing the upgrades". A window popped up saying:
> Could not install the upgrades. The upgrade has aborted. Your system
> could be in an unusable state. A recovery will run now (dpkg --configure -a).

I clicked "OK" (or was it "close"?), and the GUI was stuck at 45%. I could no longer scroll the in-built terminal output, and the GUI window appeared to be stuck.

Looking at the terminal from which I launched `kubuntu-devel-release-upgrade`, I could see

    Configuration file '/etc/apport/crashdb.conf'
     ==> Modified (by you or by a script) since installation.
     ==> Package distributor has shipped an updated version.
       What would you like to do about it ? Your options are:
        Y or I : install the package maintainer's version
        N or O : keep your currently-installed version
          D : show the differences between the versions
          Z : start a shell to examine the situation
     The default action is to keep your current version.

This launch-terminal didn't accept input. I had to kill the GUI process (from the launching terminal)

I then ran `dpkg --configure -a`, which seemed to continue where I left off, presenting me again with the above query. I presume that this hang was due to the GUI "Distribution Upgrade" window being unable to accept text input.

[1]: https://help.ubuntu.com/community/TrustyUpgrades/Kubuntu

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: ubuntu-release-upgrader-qt 1:0.219.2
ProcVersionSignature: Ubuntu 3.13.0-20.42-generic 3.13.7
Uname: Linux 3.13.0-20-generic x86_64
ApportVersion: 2.14-0ubuntu1
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: KDE
Date: Fri Apr 4 08:48:42 2014
InstallationDate: Installed on 2012-12-16 (473 days ago)
InstallationMedia: Kubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to trusty on 2014-04-02 (1 days ago)