User blog comment:KillRoy231/Villains/@comment-24066070-20140706151221/@comment-7418318-20140706185032

To paraphrase Makarov's explanation which you'll hear in the Phantom Lord arc:

"Do Fairies have tails? Do they even exist? Nobody knows and thus it's a mystery. A neverending journey."

So you see the tail is intentional and note a spelling mistake. The guild symbol too is a stylyzed fairy with a tail.