Traded Sister of Parvos gave an On Call Kuva Lich instead of intended Sister

[WarboyNux127]

I traded a Sister of Parvos with my partner (twice, because I converted instead of vanquishing), when he traded her back to me, it gave me his On Call Kuva Lich instead of the Sister. Now I have an active Lich, and no Sister. She's showing as traded on his side as well as mine. Let it be noted that he did indeed use his On Call for some of the Sister missions, but the On Call Lich is still a member of his Railjack crew and is still in his On Call. 

I don't know what happened and how, and as far as I know an On Call Lich is untradeable until they are removed from the role.