Custom Login Redirect Problem

It works fine for register and login, but when clients try to place a bid while not logged in, the site redirects them to the login page, but adds ‘&wdm-bid-val=’ with the bid amount following, which causes the link to 404 because the login page does not have that additional string. Is there any way to remove the bid val string, or fix the login link that it will redirect properly?

The page I need help with: [log in to see the link]