OK, found a solution.
As an example for the postlist jump menu:
In ubbt.inc.php
in function jump_box
Find
$query = "
SELECT Bo_Number,Bo_Title,Bo_Keyword,Bo_Cat,Bo_CatName,Bo_Sorter
FROM {$config['tbprefix']}Boards
WHERE Bo_Active='1'
$groupquery
$thiscat
ORDER BY Bo_Cat,Bo_Sorter
Replace with
$query = "
SELECT t1.Bo_Number,t1.Bo_Title,t1.Bo_Keyword,t1.Bo_Cat,t1.Bo_CatName,t1.Bo_Sorter
FROM {$config['tbprefix']}Boards AS t1
LEFT JOIN {$config['tbprefix']}Category AS t2 ON t1.Bo_Cat = t2.Cat_Entry
WHERE Bo_Active='1'
$groupquery
$thiscat
ORDER BY t2.Cat_Number ,t1.Bo_Sorter
