People should not have to work harder to see the preview -- the browser should display it automatically. Sometimes it does, but often it doesn't. That sounds like a bug to me, but maybe it's intentional as a way to conserve bandwidth.
The "bug" behavior could be dependent on what client (browser or app) you run. I offered the bit about clicking the "bookmarks" button as a workaround to the missing preview. Adding redundant additional text along with the link is another workaround.