An example

This question was asked earlier today. The accepted answer by the user "mathlove" was posted within minutes of asking.

Now consider this question. The user "mathlove" also has a very similar answer here on an effectively identical question.
While it's totally plausible that the user forgot that they posted this answer earlier on this question (hell, I myself might have a few similar answers like this), but my (cynical) self says that they chose to ignore this on purpose to gain a little extra rep because of how similar the answers look.

The question

My question is this, should we still post an answer regardless of the fact we already have an answer on a particular question if we know it to be duplicate? I personally feel it's wrong that we get a little extra rep from the same answers. What do you guys suggest?