timezone in docker alpine

According to https://wiki.alpinelinux.org/wiki/Alpine\_Linux:FAQ\#How\_do\_I\_set\_the\_local\_timezone.3F and http://www.sonoracomm.com/index.php?option=com\_content&task=view&id=107&Itemid=32, I added

    echo "CET-1CEST-2,M3.5.0/02:00:00,M10.5.0/03:00:00" > /etc/TZ

to my RUN commands in my Alpine based docker container (FROM alpine). But it does not work:

/ # cat  etc/TZ
CET-1CEST-2,M3.5.0/02:00:00,M10.5.0/03:00:00
/ # date
Wed May  4 14:15:13 GMT 2016

Actually the time should be 16:15:13. Changing the TZ content does not change anything:

/ # cat  etc/TZ
CET-3CEST-4,M3.5.0/02:00:00,M10.5.0/03:00:00
/ # date
Wed May  4 14:44:22 GMT 2016

What am I missing here?

(from redmine: issue id 5543, created on 2016-05-04, closed on 2017-05-22)