Yes I was doing some tests so the result was a bit strange on screen !!
I tracked down the problem to the sql query in the get_courses function in lib/datalib.php not having anything after the ORDERBY so you are probably right I should have used the re-sort button but I fixed it in an atrocious way adding a :
if (!$sort) {$sort="c.sortorder ASC";}
line before the query. because it was past midnight and I had to take the decision either to roll back to the version before upgrade or to solve the problem before my students wake up in a few hours.
In any case the site seems now to be OK. I go to sleep.