I've got a fresh install of the latest link code and used the ACP to add a custom field...

select * from adv_links_cfields \G
*************************** 1. row ***************************
fieldid: 1
title: TestField
description: Here is test text.
type: text
required: 0
displayorder: 1
searchable: 1
maxlength: 50
options:
catids: all
incsubs: 0
1 row in set (0.00 sec)
Then used the ACP to add a link.

select * from adv_links_cfields_entries \G
*************************** 1. row ***************************
lid: 1
field1: perhaps
1 row in set (0.00 sec)
I verified the field appeared as expected under the Link Details. Then I went to search against that field. If I include that field in a broader search, I can search against it. If I uncheck all other fields, and only leave checked my new custom field, the search fails...

Warning: array_merge() [function.array-merge]: Argument #1 is not an array in /var/www/vb3/l/search.php on line 90

Warning: implode() [function.implode]: Bad arguments. in /var/www/vb3/l/search.php on line 94

Warning: Invalid argument supplied for foreach() in /var/www/vb3/l/search.php on line 111

Warning: in_array() [function.in-array]: Wrong datatype for second argument in /var/www/vb3/l/search.php on line 132

Database error in vBulletin 3.6.4:

Invalid SQL:

SELECT links.linkid
FROM adv_links AS links

LEFT JOIN adv_links_cfields_entries AS customfields ON (links.linkid = customfields.lid)
WHERE suspended = 0 AND () AND valid = 1
LIMIT 500;

MySQL Error : You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ') AND valid = 1
LIMIT 500' at line 5
Error Number : 1064
Date : Monday, February 19th 2007 @ 09:12:58 AM
[snip]
Sorry if this is a repeat: I had a tough time getting past the CAPTCHA prompt only to find out I can only search against titles. I didn't find anything that looked relevant to this issue.