Kingdraiko

When I trade a Pokemon with my girlfriend, my new Pokemon goes straight into the PC but hers goes to her party. The other day I traded her a Kadabra for her Haunter. The Haunter went to my PC so it didn't evolve but the kadabra went to her party and became an alakazam. We had the same number of Pokemon in our party. This also does it with NPCs and everyone else I trade. Can someone tell me how to fix this? Thank you