Same thing happened to me. Didn't cost me the game, but it could have been relevant. It happened twice in the same game. The second time around I realised I should record it so I did, altough I didn't manage to record from the very beginning. Regardless, it shows that the spell is on the stack and the opponent is choosing the name before the card ETBs. By the time it is actually on the battlefield, the name has been chosen.
Same thing happened to me. Didn't cost me the game, but it could have been relevant. It happened twice in the same game. The second time around I realised I should record it so I did, altough I didn't manage to record from the very beginning. Regardless, it shows that the spell is on the stack and the opponent is choosing the name before the card ETBs. By the time it is actually on the battlefield, the name has been chosen.