timestamp+interval across a DST boundary gives erroneous result

[Raphael Mankin]

I am adding INTERVAL '1 day' to TIMESTAMP WITH TIME ZONE '2017-03-25 12:00 Europe/London'. This timestamp with chosen quite bloody mindedly as the arithmetic crosses the DST boundary. (I am testing other software that generates SQL).

Oracle, Vertica and Presto (with a pg back-end) all give a result of 13:00 on 26March; Raw Postgres give 12:00 on 26March, i.e. it adds only 23 hours. Changing INTERVAL '1 day' to INTERVAL '24 hours' yields 13:00.

demo_db=> SELECT TIMESTAMP with time zone '2017-03-25 12:00:00 Europe/London' + interval '1 day' ;
        ?column?
------------------------
 2017-03-26 12:00:00+01
(1 row)

demo_db=> SELECT TIMESTAMP with time zone '2017-03-25 12:00:00 Europe/London' + interval '24 hours' ;
        ?column?
------------------------
 2017-03-26 13:00:00+01
(1 row)

PostgreSQL 9.5.5 on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 6.2.0-5ubuntu12) 6.2.0 20161005, 64-bit

ProblemType: Bug
DistroRelease: Ubuntu 16.10
Package: postgresql 9.5+176+git1
ProcVersionSignature: Ubuntu 4.8.0-34.36-generic 4.8.11
Uname: Linux 4.8.0-34-generic x86_64
ApportVersion: 2.20.3-0ubuntu8.2
Architecture: amd64
CurrentDesktop: XFCE
Date: Tue Jan 24 15:01:08 2017
InstallationDate: Installed on 2017-01-15 (9 days ago)
InstallationMedia: Xubuntu 16.10 "Yakkety Yak" - Release amd64 (20161012.2)
PackageArchitecture: all
SourcePackage: postgresql-common
UpgradeStatus: No upgrade log present (probably fresh install)

[dino99 (9d9)]

This is an unsupported release now. Please think to install the next LTS 'Bionic 18.04'

http://cdimage.ubuntu.com/ubuntu-next/daily-live/current/
https://www.omgubuntu.co.uk/2018/02/ubuntu-18-04-minimal-install-option