Yep that is odd, I played that part before R3 V1.00 and I got the scene with Seraphina but I didn't tried it with the latest version. Before people start blaming mods, I played with them and got the right scene at that time. I save a lot so let me check a older save before that event and see what happens. I'll edit the post later.
Edit: Just checked both my saves allied with witches and demons and I get the right scene (after a sex scene with Leyala right?) with Seraphina with witches and Kagome with demons. So yeah something odd happened with the variable in your game on that scene sequence. If you use URM you actually can check what variable is called before entering the scene, I usually don't use URM in my favorite games (only author specific for that game mods) so can't really say when the variable (sided with witches/demons) is called.
Edit 2 : I placed URM (will remove after close the game, don't want to play 1 of my fav games with it hehe) just to check when the variable is called and it appears in last render of Leyala sex scene (if you skipped that scene then probably appears in a different render just before start either the scene with Seraphina/Kagome) and it is something like this in my Sided with Witches save, the condition "sided with demons" is false and then enters the scene with Seraphina that in this case is labeled r3s19b (the sided with demons is label r3s19, it is covered by the visibility condition). Check spoiler below.
