I think there is a general practice in place that when duplicate answers are posted, the slower users will defer to the faster one by means of upvote and a deletion of their own answer. When this doesn't happen, both answers get upvoted when only one answer is necessary. (In this particular instance there are four virtually identical answers that have all been upvoted).
Should we encourage the slower user to delete their own question if they fail to do so? Is this even a problem?