A "shortlink" is a URL (website address) that's been shortened using a service such as Goo.gl or Bit.ly. Shortened URLs can more easily be shared, tweeted, or emailed.
The trouble is, if you use a shortlink to visit a website you have whitelisted, you will not see the ads right away. The same thing happens if you come to a whitelisted site by clicking a link on a different site.
This looks like a bug but it isn't. When you visit a whitelisted website, AdBlock looks in your custom filters for an exception rule (that is, a whitelist rule) for that domain. If AdBlock doesn't find one, it continues blocking the ads on the site.
Let's say you have whitelisted some-really-long-address.com, for which you also have the shortlink goo.gl/x812zY. The exception rule is @@||some-really-long-address.com/$document. Similarly, let's say you have whitelisted news-site.com. The exception rule for that is @@||news-site.com/$document.
When you go directly to some-really-long-address.com or news-site.com, AdBlock finds the rule "@@||some-really-long-address.com/$document" or "@@||popular-social-site/$document" and knows not to block the ads on that site.
When you visit the same page with a shortlink or by clicking a link on say, popular-social-site.com, however, the redirecting domain (that is, goo.gl or popular-social-site.com) doesn't appear in your custom filters. AdBlock doesn't know it's supposed to be allowing ads on the page you're going to.
You probably don't want to whitelist all of goo.gl or popular-social-site.com! The workaround, then, is to refresh the page when you get to it from a shortlink. That will let AdBlock "read" the actual domain name, find the site's whitelist rule in your custom filters, and allow the ads to appear.