Bug: Selecting cards with Karn, the Great Creator while controlling a player

Per Gatherer, on Emrakul, the Promised End's page: "Controlling a player doesn’t allow you to look at that player’s sideboard. If an effect instructs that player to choose a card from outside the game, you can’t have that player choose any card."

However, earlier today in a game, I was able to view my opponent's sideboard and select a card from it with Karn's effect while controlling them with Emrakul's effect. Given this ruling, I'm fairly certain that's not supposed to be the case.

Start by reproducing the interaction between Emrakul, the Promised End and Karn, the Great Creator described in the report, then trace the handling of selecting cards from outside the game while controlling another player. Done means the controlled player cannot view or select a card from the opponent’s sideboard in this situation, consistent with the cited ruling.

Written by the indexing model from the issue text.