From my understanding, the PvP search thing is a little bugged.
I've tried just to see what happened, taking 3/4 accounts and making them pvp duel each other.
So, P1 challenges P2, P2 challenges P3, P3 challenges P1.
What always ends up happening is 2 players end up playing each other, and the third gets ignored.
Also, the PvP search is a little out of synced, one person will always get the You are playing .... Message before the other.
I assume the system works a bit weird, because instead of creating a host and a joiner, you get the server randomly pulling people into a gameroom. I guess some discrepancies can cause you to play yourself or get in to a 3 player game, which is probably another cause for desyncs.