In MVC, you can't assume the last slash is the root of the site as you could with webforms. If your site is running in "/store" and you're using hard-coded URLs, you must ensure that all of your URLs start with "/store/". Starting a URL without a leading slash will root your URL's differently depending on if your topic is called from "/store", "/store/topic/hometopintro", or "/store/fancy/custom/url".
Obviously, the correct solution is to avoid hard-coded URL's. If that's not possible, a site could resolve this by creating a rewrite rule that redirects "/store" to "/store/", but that will only work for the homepage.