What a clodsburger I am. The problem was had left the old name in
Setup.php, (which I need for two wiki on earlier Debian.)
Maybe some warning could be printed ... OK, never mind. Close the bug
I suppose, if not closed already.
Here was some stuff I wrote just before discovering the cause:
Yes, changing $wgSitename has instant effect that
all users can see. The problem is e.g.,
$ php dumpBackup.php --current|sed -n '/sitename/{;p;q;}'
still shows the old name!
(Same with namespace 4 and 5 ($wgMetaNamespace no help.))
update.php doesn't help.
Special:Export works fine though.
deleteBatch.php and moveBatch.php will only operate on the old name.
Now I have cleaned up Setup.php and all is OK. Maybe some
informational messages could be printed...