Hello,
I am looking into this situation, but this is not, as was previously just mentioned, just a visual bug. Please disregard that. I suspect that these are the computer-generated arena teams added to the arena function to help new servers that may lack enough population to find consistent matches, but I am not positive about that, and am seeking clarification from the developers. However, I have not yet heard word back. I will let you know as soon as I have confirmation one way or the other.
Thank you for your patience regarding this issue!