You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
Prefix Essentials 2.5.1
Change log
Added an admin option to
force the prefix of question type threads to have a specified prefix and
force the prefix of solved question type threads to have a specified prefix
/admin.php?options/groups/prefixess/
Release notes
The idea is that it's easier then for people to find question and solved threads using prefixes.
Note that using this setting overrides prefixes added on thread creation and when a question thread is marked as solved or unsolved.