Keeper League Dispute About Traded Draft Picks

Making this post for a friend who is in this situation.

He's in a keeper league where you can keep guys but have to give up the draft round of the player you keep (standard stuff I think). New league-- started last year.

He traded Puka for a second round pick last year and now the owner he traded with wants to keep his second round player. The commissioner says that "you can always keep a player" and that because he's keeping his second round player, he will get the next pick the player has available, which happens to be his fourth rounder.

I told my friend that I thinkj the other owner shouldn't be able to keep his second round player (or should have to spend his first on him). I don't play in any draft keeper leagues (I do an auction one) and so was curious if this was normal or not.