Custom ajax Search Field Not Populating After Upgrade

Hello -
We recently upgraded from 1.3.8 to 1.3.9b.
Our Search feature has three fields. When a search is FIRST tried, the second field does not load/populate. BUT after a failed attempt, and the message that all fields need to be selected, this field will NOW populate. Any ideas? Is there a search-related php file I should bring over from my old version? I've already brought over several search-related files, but no help yet.
To test: https://www.saddlemen.com/store
A valid test search is: Harley-Davidson / Touring / 2009
You can see the bug.
Thanks in advance!

Well, if no ideas are coming to mind out in the ZC community, as a work-around, I'd like to put a line of text under the header, politely asking searchers to reload if they have trouble.

Can I add a line of text to my "tpl_advanced_search_default.php"?

Thanks in advance...

I'm not programmer enough to point to the problem, but IE says you have an error in your code - "Object Expected" on line 228, which seems to be this line here:

<select name="manufacturers_id" onchange="xajax_GetModelWrapper(this.value);">

Thanks STEVESH!

You spurred me to look at the source code of the NEW search page, then to do a brief reactivation of 1.3.8, and printing the source for the OLD (working) search...

The old version has a major string of code (over 40 lines!) that are dominated by "xajax" and javascript listings. Ugh.

Thanks for looking into things. Anyone with further, ideas, please feel free to chime in.

Eric
https://www.saddlemen.com