So insert is
bnl@ibm2:~/db$ psql
Tidtagning är på.
AUTOCOMMIT off
psql (9.6.15, server 9.4.15)
Skriv "help" för hjälp.
Except you are using psql 9.6.15 against a 9.4.15 server.
What happens if you use psql(9.4.15) to do sort query against 9.4.15 server?
So this is more than strange
bnl@ibm2:~$ /usr/lib/postgresql/9.4/bin/psql
Timing is on.
AUTOCOMMIT off
psql (9.4.15)
Type "help" for help.
This. works. I did not realize I ran different client/server versions.
9.6 must have come with a Debian upgrade where I did not migrate the database to 9.6,
but got the psql 9.6 as default (/sr/bin/psql)
However AFTER I checked the bad sorting - sep/oct 2016 and early apr 2017
With psql 9.4 I connected with psql 9.6 again.
And now the sorting error is gone her too!
I cannot reproduce it anymore
So I learned this - always use same version of client and server
Many thanks to Adrian and Tom