Originally Posted by
fastair
Looks like you are searching for 1 tkt on 1st window and 4 people on 2nd. Trying making those variables the same.
This. Odds are that the return doesn't have 4 tickets in the same fare class, and the way that I've seen UA.com work is that if there aren't enough tickets in a fare class for the whole PNR it moves all passengers into the higher fare class.