New arena rules have been specified in the
FAQ.
Pay special attention to:
4. No two characters who have recently (this season) been controlled by the same person and are on different teams may queue at the same time and risk facing each other. The matchmaking system will only prevent characters from facing each other if they currently have the same IP address. The e-mail method used prior was being abused. So if you are whoring your char out (also against the rules, though not in itself bannable) and the other person queues and your two characters face each other, you and possibly your entire team will be disqualified for the remainder of the arena season.
There will be a 1 week grace period starting now, ending on the 8th, where if you are found to be doing this you will receive 1 warning.
Please report anyone you suspect of breaking this rule and it will be investigated.