Moving characters between parties

[TheSapient]

I wanted to add an experienced character from Party A to Party B.  Party A is further along the story than Party B.  In the Party B Manage Party screen, the character was available (not shaded out nor locked), so I dragged her into Party B, and then went into the Manage Decks to trade some cards with other Party B Characters.

 

But now it seems that this character is in both parties, with slightly different decks.  Did I make a copy of her that can develop independently?

 

I just don't understand character management in this game.