I don't think it's an issue when there are multiple people cosplaying the same character but there always seems to be an awkward tension when they first see each other especially if it's a rarely cosplayed character. It seems like they have to size each other up before they move on. :P
One really awkward thing for me was when my husband cosplayed as Cloud. An Aeris cosplayer kept flirting with him and it took so much for me not to jump in and stop her. Even after mentioning he had a wife she was still flirty. I kinda get that she may have been 'in character' but it was still pretty weird.
"I see now that the circumstances of one's birth are irrelevant; it is what you do with the gift of life that determines who you are."