Commit error - QApt Batch Installer while applying changes from --install firefox-local-en

The day after upgrading Kubuntu to 14.10, KDE displayed some notifications of updates available, I wasn't sure if from the upgrade or something later. I clicked Muon updater and its Software Updates window said "The software on this computer is up to date".

But when I closed that, there were two dialogs on-screen (see attachment):
  Installation Complete
  Package installation failed.

and
  Commit error- QApt Batch Installer
  An error occurred while applying changes:
  [No details when I click Details>>]

In the process list I see
  F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND
  0 1000 5161 2507 20 0 361508 97468 poll_s S ? 0:05 qapt-batch --install firefox-locale-en

I usually run SeaMonkey (I'm reporting this in SeaMonkey) but do have Firefox available.

I don't know if this is residual issues from my Kubuntu 14.04 update (I earlier filed #1385791 and #1385620), or a problem with the Muon package updater (the dialogs remain whether I open or close muon-updater), or something else.

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: qapt-batch 2.2.0-0ubuntu2
ProcVersionSignature: Ubuntu 3.16.0-23.31-generic 3.16.4
Uname: Linux 3.16.0-23-generic x86_64
ApportVersion: 2.14.7-0ubuntu8
Architecture: amd64
CurrentDesktop: KDE
Date: Sun Oct 26 13:36:36 2014
SourcePackage: libqapt
UpgradeStatus: Upgraded to utopic on 2014-10-26 (0 days ago)