One bug I found when helping track down a conflict a user of one of my hacks was having with this modification was the following:
In the plugin
Prefix: Query Prefix in Search Forums (Thread) the variable
$hook_query_fields is being declared instead of appended. This will cause conflict with any modification using this same hook location. So, in order to properly fix this replace the contents of the plugin with:
Prefix: Query Prefix in Search Forums (Thread):
PHP Code:
$hook_query_fields .= ', thread.threadprefix';
Note the addition of a '.' (period) before the '=' (equals).
That should do it.