I've just realized that I did not changed the category of the issue. It must be "filters". Sorry for that.

I confirm the same issue ou our Mantis system.
It appeared when we switched from version 1.01 to 1.05 final.

I've got the exact same problem ( after upgrading from 1.0.4 to 1.0.5 )

I can confirm this issue as well at bugs.unrealircd.org.
Simply put: clicking any of the sort buttons does not influence the sort order (Even though 'the arrow' etc is shown).

It happened after we moved servers... New one has PHP5 and maybe also a more recent MySQL.

After noticing this issue I upgraded from 1.0.1 to 1.0.5, still same issue. So I would say it's not some bug introduced in a recent version, but maybe more of a PHP5 issue ?

Oh, sorry for that, we switched from PHP5 CGI to mod_php (which we were at, at the previous server), which means we're back at PHP 4.4.3. And still experiencing this problem. So I guess not related to PHP 5 then after all.

EDIT: On a side note, we're now back at PHP5 again ;P

The actual reason is in MySQL. Sorting problem appeared after upgrade from 4.1.19 to 4.1.21. In more details:
Sorting in SQL querys like

SELECT FROM table WHERE id=5 OR id=6 OR id=7 ORDER BY some_field
or
SELECT FROM table WHERE id in (5,6,7) ORDER BY some_field

doesn't work! This causes problems because such query is used for sorting. In upcoming 4.1.22 there are a lot of fixes deal with ORDER - suppose this case also would work.

nod @ MySQL issue

References for this MySQL bug:
http://bugs.mysql.com/bug.php?id=21992 (dup of next)
http://bugs.mysql.com/bug.php?id=21456 (says it's fixed now, but no new version released yet)

Can one find earlier versions of mysql to download? I couldn't find them 4.1.19 on the MySQL site.

This seems to be a workaround:

alter table mantis_bug_table ADD INDEX (id);
alter table mantis_bug_table DROP PRIMARY KEY;

Fixes the sort order :)

did someone test the proposed solution in note (0013623 by syzop)?
Does not it has side effect on bug creation: The id is incremented correctly?

We've been running with this for 2 weeks now, without any problems. Had 8 new bugreports. Yeah id seems to increment ok. Haven't seen any errors or other weird behavior showing up.

The problem has been fixed in 4.1.22, which has been released already.

Confirmed that mySql 4.22 fixes the problem... I can't change the ticket stauts!