Product Fields cannot be changed

In admin/store/settings/products/edit/fields, I tried to set the fields that will be displayed on the product page, but after submitting the form, the checkboxes return to default values. Checked the db, and there seems to be no sign of the uc_product_field_enabled variable.

My setup:

Array
(
    [site_id] => 
    [server_name] => 127.0.0.1
    [php_version] => 5.2.10
    [drupal_version] => 5.20
    [db_type] => mysql
    [db_version] => 5.0.67
    [ubercart_version] => 5.x-1.8
)

Tried resubmitting the form, but the default values are still selected. Tried to manually add the uc_product_field_enabled variable manually (from my other sites) and still no luck.

Any ideas? Thanks!