I merged two topics because they were duplciates of bug reports in our system. I wanted to comment on the duplicate, to explain why I was merging them. So I unmerged them. Now the duplicate is gone, and its link still points to the merged (now unmerged) topic.
Duplicate: http://smart-support.acrobatiq.com/topics/264-white-space-in-callout-with-images/ (I took this URL from my notification email)
When I follow the second URL I'm redirected to the first one.