You have been subscribed to a public bug by Flames_in_Paradise (ellisistfroh):

[ Impact ]

People in certain timezones have buggy time conversions in all Qt apps.

[ Test Case ]

See bug report.

[ Regression Potential ]

Should be low, in upstream LTS release and includes unit tests during
build time.

--- original bug report ---

For a set of timezones in tzdata-2016*
Qt parser produces wrong result in
Qt versions earlier than 5.6.

In kubuntu-16.04 xenial xerus the most annoying
issue is broken digital clock plasmoid on the default KDE panel
if system timezone is set to e.g. Asia/Novosibirsk.
All Qt programs that attempts to convert time to non-default
timezone are affected as well in xenial and earlier ubuntu released
including ubuntu-14.04 LTS trusty.

I consider the bug is nasty enough for updating Qt in LTS ubuntu

The upstream bug is
"QTimeZone mishandles tzdata 2016b and later in Russia, Kazakhstan".
The direct link to the patch that fixes the problem is;a=patch;h=e9041c7fc1052167f1ec2df0ea9623059e55d00f

I have rebuilt qtbase-opensource-src-5.5.1+dfsg (-16ubuntu7.1)
from sources with the patch applied and the bug has gone away.

A bit more details.

I faced the problem with Kubuntu 16.04.1, x86_64.
Asia/Novosibirsk has UTC+07:00 offset last a couple of months
but KDE clock shows a time that has offset of 14 hours from the actual wall 
so it is rather unusable.
Command line tool "date" reports correct local time.
KDE digital clock works correctly in e.g. Asia/Krasnoyarsk timezone.
It as a workaround if time transition history does not matter.

Some other timezones affected by the bug (tzdata-2106f)
file europe:
file asia:

A simple program to demonstrate the problem:

#include <QDebug>
#include <QTimeZone>
#include <QDateTime>

int main() {
        QTimeZone tz = QTimeZone(QTimeZone::systemTimeZoneId());
        QDateTime current = QDateTime::currentDateTime();
        qDebug() << "current offset" << tz.offsetFromUtc(current);
        return 0;

It reports 0 for incorrectly parsed timezones.

The only thing that bothers me is that I had to disable tests
when was rebuilding libqt5core5a_5.5.1+dfsg-16ubuntu7.1_amd64.deb
using dpg-buildpackage. Otherwise I got error with cmake
in tests/auto/cmake/. Cmake was unable to find qt libraries
in the build tree.

** Affects: qtbase-opensource-src (Ubuntu)
     Importance: Undecided
     Assignee: Timo Jyrinki (timo-jyrinki)
         Status: Fix Released

** Affects: qtbase-opensource-src (Ubuntu Xenial)
     Importance: Undecided
     Assignee: Timo Jyrinki (timo-jyrinki)
         Status: Fix Committed

** Tags: kubuntu patch verification-needed xenia
timezone parser in qt-5.5 breaks KDE clock
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