Two threads on the same topic constitutes a duplication. We're pretty lax in the rule department around here, and there's no rule that says you can't post 2 links in a topic when both links are on the same topic.
There's no rule that says you can't have a duplicate topic, either, but as with all other things under the heading of free speech, expect consequences. When people ignore a duplicate topic, no rule states that you gotta whine about what you shoulda seen coming a mile away.