[Koha] Wrong order wehen sorting public list by copyright year

[Michael Kuhn]

Hi

We are working with Koha 18.11.05 on Debian GNU/Linux 8.

In our library we found in the OPAC it is not possible to sort public 
lists correctly by copyright date.

As far as I know sorting by copyright date would follow the content of 
MARC 008 position 7-10. But looking at an actual sorting we see the 
sorting is as follows

2018
2017
2016
2015
2015
2014
2014
2013
2011
2017 <-- here it starts getting wrong
2019
2018
2016
2018
2016
...

Alle these records have correct content in MARC 008 and MARC 264$c.

Strangely we found if a record has content in MARC 260$c and 264$c it 
changes the sort order - even if only MARC 008 should be relevant for 
the sort order.

How can we achieve the correct sort order?

Best wishes: Michael
-- 
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