This might be a duplicate of bug #1509655. If /var/log/dist-upgrade/main.log ends with a python backtrace pointing to DistUpgradeViewKDE.py line 339, it is the same problem.
This might be a duplicate of bug #1509655. If /var/log/ dist-upgrade/ main.log ends with a python backtrace pointing to DistUpgradeView KDE.py line 339, it is the same problem.