I've seen this happen a few times, when starting a random team match, the team numbers will not be even--once I was the one in a one vs. two match, and I've seen 3 vs 4. In the case of the 1 vs 2, players started joining mid-match, which seemed rather odd, until it was 4 vs 4--not in the case of the 3 vs 4 match, though.
Is this intentional, or a bug? Shouldn't teams always be equal numbers?
Things also could affect that like players leaving the area which would cause the parties to be not equal.