Steps to reproduce the issue

Create an element with plugin cascadingdropdown with autocomplete enabled.
If "Render As" is Dropdown the query is right.

Expected result

Generated query:

SELECT DISTINCT(source_dirs.path) AS value, source_dirs.pathAS text
FROM source_dirs AS source_dirs
WHERE source_id IN ('5') AND source_dirs.deleted=0

Actual result

Generate sql query is missing the WHERE clause, causing in a full table download:

SELECT DISTINCT(source_dirs.path) AS value, path AS text
FROM source_dirs AS source_dirs
ORDER BY text ASC

System information (as much as possible)

Linux 3.10.0-327.el7.x86_64 #1 SMP Thu Oct 29 17:29:29 EDT 2015 x86_64 (RHEL 7)
Database Version | 5.5.5-10.1.21-MariaDB
Database Collation | utf8_general_ci
Database Connection Collation | utf8mb4_general_ci
PHP Version | 7.1.1
Web Server | Apache
WebServer to PHP Interface | apache2handler
Joomla! Version | Joomla! 3.7.5 Stable [ Amani ] 14-August-2017 12:09 GMT
Joomla! Platform Version | Joomla Platform 13.1.0 Stable [ Curiosity ] 24-Apr-2013 00:00 GMT
User Agent | Mozilla/5.0 (Windows NT 10.0; WOW64; rv:54.0) Gecko/20100101 Firefox/54.0

Additional comments

See Forum post