I haven't seen this happen before. I just reviewed Ann Douglas's latest story, and almost at the same time Jetcrash747 also reviewed it. Is this an omen of something? Maybe my reviews are superfluous? I try not to duplicate reviews when a story has been reviewed before. Well, Dance of a Lifetime, but the last review was several years ago, and I had some alternate titles that I thought were funny and wanted to get them in print.
Duplicate reviews tend to waste bandwidth, unless they conflict in some way, or one offers more or better information than the other. I don't know how to prevent this kind of duplicate effort. Maybe I should wait for a couple of weeks to see if someone else thinks a story is worth recommending.
We could try to set up a clearing house here on this forum, where a reviewer indicates he is preparing a review, so other reviewers work on other stories. I am not quite sure how that would work in practice. Maybe its better if we all race to do our review first, so if the story gets multiple reviews, readers will get the idea its a really good story.