I am using the Google Webmaster Tool for testing the robots.txt initially.
Specifically the "Crawler Access" under "Site Configuration".
When I test the following you provided:
The result come back Allowed.
When I add the / :
The results come back Disallowed. Blocked by line 2: disallow: /products_results.php
But regardless of the above settings in the robots.txt file when I use the Search Engine Visibility tool it some how finds all links. (897 of them)
This tools must be ignoring the robots.txt and meta tags.