WordPress – Reserved form field names?

I have installed a simple PayPal Cart plugin:

http://wordpress.org/extend/plugins/wp-ultra-simple-paypal-shopping-cart/

Installed just fine. However, when updating a quantity or anything that involves the posting of a form, WordPress returns a 404 error page.

Now, when investigating, I noticed someone mentioned that WordPress has some reserved words for form field names internally.

( http://wordpress.org/support/topic/404-pops-after-custom-form-submission-by-post )

I followed this trail and altered the name fields with Firebug on the fly and post the form.

Everything was post to the current page and it stayed on the same page (as expected) instead of the 404. So it seems that this IS indeed a WordPress issue.

Is there any way I can add exceptions to certain names in WordPress as a setting of some sort? Or if anyone knows a work-around for this plugin, I’d much appreciate it.

Many thanks for your input.
Michael.

EDIT:

Someone has also had this problem. See this thread…

http://www.ultra-prod.com/developpement-support/wp-ultra-simple-paypal-shopping-cart-group3/bugs-errors-help-forum8/404-error-thread76/

Any idea on a solution? I can’t simply rename my post type. This is for a website that’s already in production and has hundreds of products.

Hope someone can help.