Moving captured specialists

I just saw a player send a captured specialist to it's owner, and I don't know how it could have happened. Here are the details:
Player 1 had a mine with player 2's captured assassin. Player 1 then sent a sub with the captured assassin and nothing else to player 2's outpost. Once it gets there, the assassin will reactivate for player 2. I see player 2's entire base, and he hasn't had any diplomats (although he does have one available to purchase from his queen). Even if there was a diplomat involved, wouldn't the sub be in player 2's color, with the assassin being released immediately upon leaving the outpost?
Was this a bug, or is there some way this could have happened that I'm not thinking of?
Player 1 had a mine with player 2's captured assassin. Player 1 then sent a sub with the captured assassin and nothing else to player 2's outpost. Once it gets there, the assassin will reactivate for player 2. I see player 2's entire base, and he hasn't had any diplomats (although he does have one available to purchase from his queen). Even if there was a diplomat involved, wouldn't the sub be in player 2's color, with the assassin being released immediately upon leaving the outpost?
Was this a bug, or is there some way this could have happened that I'm not thinking of?