UT 3rd round: who plays?

In a user tournament in the 3rd round sometimes we have to deal again with the 2nd placed players. Is this always? Is it a choice of the creator? Is it random?

I wonder why it happens...

uh. I love UTs, so I will try to answer.

I am not 100% sure, but I think that in EACH round the best TWO players are promoted to next step. That's all