blacklist

  That's pretty much the same experience I've had, even with vanilla followers.  Sometimes, the follower even assaults the player on her own.  Is a particular follower framework necessary/recommended?

  According to the code, it should happen 30% of the time that the SanguineRape function is called (which is often).  You should see "Show me what you can do with your friend here..." if a player/follower scene is about to occur, or "Let's see what your friend is capable of..." if your master decides to take your follower for himself.   I've never actually seen it happen, though.  The only time I've seen a follower get involved is when they're assaulting the player.  I suspect there's something interfering with how the mod is seeing followers, and causing them to register as bystanders instead of potential victims.  I'm not experienced enough in Papyrus to figure it out, though.