du --time reports wrong time

[Alun Perkins]

expect
du --time --time-style=+%s theFile
to give modification time of theFile expressed as seconds since the epoch.
Comparison to "date" shows that du is reporting the time wrongly.
This script:

echo "my time and time zone:" $(date)
touch timestampTest
echo "date says: " $(date -r timestampTest +%s)
echo "du says:" $(du --time --time-style=+%s timestampTest)

has this output:

my time and time zone: Fri 26 Aug 10:12:38 BST 2016
date says: 1472202758
du says: 0 1472206358 timestampTest

the times are different (an independent check of the time shows that date is correct, so du must be wrong).

Note that on the other hand, human-readable time DOES work correctly for du.
input : date -r timestampTest +%c
output: Fri 26 Aug 2016 10:12:38 BST
input : du --time --time-style=+%c timestampTest
output: 0 Fri 26 Aug 2016 10:12:38 BST timestampTest
These are the same, as expected.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: coreutils 8.25-2ubuntu2
ProcVersionSignature: Ubuntu 4.4.0-34.53-generic 4.4.15
Uname: Linux 4.4.0-34-generic i686
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: i386
CurrentDesktop: KDE
Date: Fri Aug 26 10:29:55 2016
InstallationDate: Installed on 2012-09-28 (1427 days ago)
InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release i386 (20120817.3)
SourcePackage: coreutils
UpgradeStatus: Upgraded to xenial on 2016-08-19 (6 days ago)