[Plugin: WP Custom Fields Search] 404 Error in IE7 and 8

The WP Custom Fields Search plugin has been working out well for me. However, I just encountered an odd issue:

The search field I created with it works perfectly in every browser I’ve tested it in on a Mac and in Windows 7, except for in Internet Explorer 7 and 8. It works fine in 9. I’m just not sure why or what I might be able to do to get it to work in those stupid old browsers. My search field preset ‘professionals’ is setup like this:

1. “Keywords” | Data Type: Post Field | Widget: Text Input | Compare: Words In
2. “Professionals” | Data Type: Post Type | Widget: Hidden Constant | Compare: Equals | Constant Value: professionals

And I called it on a special page template using this:

<?php if(function_exists('wp_custom_fields_search'))
	wp_custom_fields_search(); ?>

So it’s supposed to search only within my custom post type “professionals” and return matches from anything. To be clear, I can SEE the search field in every browser, but just in IE7 and IE8 it’s not returning any results.

I did notice that IE7 and IE8 are lacking “&search=Search” in the search string in the URL, and when I manually add it, the search works. Here’s the “good” search string from other browsers:

?search-class=DB_CustomSearch_Widget-db_customsearch_widget&widget_number=preset-default&study_company-1=professionals&cs-all-0=davis&search=Search&site_section=professionals

And here’s the string from the same search in IE8:

?search-class=DB_CustomSearch_Widget-db_customsearch_widget&widget_number=preset-default&study_company-1=professionals&cs-all-0=davis&site_section=professionals

Is this a product of the plugin, or possibly something else? Is there some way to include this missing element for only older IE browsers? Thanks!