Question of the Week: An owner in my league will have 39 players instead of 40 when our draft ends soon. He did trade away a player for 2 draft picks. Can you explain what happened to me?
Answer: If an owner decides to trade away a player he just drafted, he may do so, but the draft board will not update mid-draft to add picks for traded players. If you have the player pool open at the end of the draft, your owner should be able to fill any open spots that remain.
The other thing you can do if you want to allow this owner to fulfill the spot they have open, is to have them tell you who they want to draft when it should be their pick had they not traded. Then you can broadcast to the league that that player is off limits, and at the end of the draft, you can use League Settings > Edit Rosters to add that player to the team.