I viewed this topic on Meta on May 26th and the preview was working, now it is not. The preview in the first post will show up if you try replying to that topic (or this topic), and pasting any imgur galley URL into the edit box, but you won’t see a preview for the URL you just pasted. The preview won’t be there if you refresh the page.
I saw the same behavior on a forum hosted at Communiteq (formerly DiscourseHosting) also on May 26th, when they were running 1.2. The behavior is still there this week with 1.3.
Hmm, that doesn’t explain why it was working here but not at my Communiteq (formerly DiscourseHosting) forum at the same time (on May 26th). Is this broken until Imgur changes something back, or until Discourse releases a fix?